Hairdressers’ shoulder load when blow-drying – Studying the effect of a new blow dryer design on arm inclination angle and muscle pain

Hairdressers’ shoulder load when blow-drying – Studying the effect of a new blow dryer design on arm inclination angle and muscle pain

International Journal of Industrial Ergonomics 74 (2019) 102839 Contents lists available at ScienceDirect International Journal of Industrial Ergono...

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International Journal of Industrial Ergonomics 74 (2019) 102839

Contents lists available at ScienceDirect

International Journal of Industrial Ergonomics journal homepage: www.elsevier.com/locate/ergon

Hairdressers’ shoulder load when blow-drying – Studying the effect of a new blow dryer design on arm inclination angle and muscle pain

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Morten Wærsteda,∗, Henrik Enquistb, Kaj Bo Veiersteda a b

Department of Work Psychology and Physiology, National Institute of Occupational Health, PO Box 5330, Majorstuen, N-0304, Oslo, Norway Division of Occupational and Environmental Medicine, Department of Laboratory Medicine, Lund University, 221 85, Lund, Sweden

ARTICLE INFO

ABSTRACT

Keywords: Hairdresser Arm elevation Ergonomic intervention Blow dryer design

During nine months, nineteen hairdressers every second/third month switched the use between a blow dryer with traditional design and one with a new design. The new blow dryer had the possibility to change between two opposite directed air flows. Every second/third month arm inclination angle and upper trapezius muscle activity were measured a whole workday, and during blow-drying in the laboratory. Pronounced upper arm elevation was reduced with the new blow dryer. The muscle activity of the upper trapezius was only reduced in the laboratory, and daily pain reports were not significantly influenced at all. The subjective rating of time use, functionality and heaviness was less favourable for the new blow dryer, with only three out of nineteen preferring the new dryer at the end of the study period. However, the design of the new dryer demanded a change of work technique that might have been conceived as problematic by the experienced hairdressers. Relevance to industry: We studied a new professional handheld blow dryer designed to allow less postures with elevated arms, addressing an import risk factor for work-related musculoskeletal problems. Hairdressers using this new dryer had less time with upper arm in pronounced elevation during blow-drying.

1. Introduction Musculoskeletal complaints are common among hairdressers (Bradshaw et al., 2011; Cruz and Dias-Teixeira, 2016) and are one of the major causes for sick leave and early retirement from the profession. Compared to non-hairdressing (mainly office) workers, hairdressers report significantly more work-related shoulder pain, wrist/arm pain, lower back pain and leg/foot pain (Bradshaw et al., 2011). Hairdressing work tasks imply to a certain degree work with elevated arms, a wellestablished risk factor for musculoskeletal shoulder complaints (van der Molen et al., 2017; Svendsen et al., 2013; Bodin et al., 2012; Hooftman et al., 2009). In a study by Wahlström and co-workers (Wahlström et al., 2010) 28 hairdressers had 2-4 full workday measurements of upper arm inclination angle, with a median upper arm inclination angle of 22° and the upper arm above 60° for 6% of the work time. Veiersted and co-workers (Veiersted et al., 2008) measured upper arm inclination angle in 33 hairdressers during 2–3 h ordinary work in their hair salons and found a median upper arm inclination angle of 30°, with the upper arm elevated above 60° for 13% of the recording time, and above 90° for 2–3% of the recording time. These figures correspond to what Svendsen and co-workers (Svendsen et al., 2004) found in 72 male manual workers: Work time above 60° were 6–7% for machinist ∗

(n = 26), 10–11% for car mechanics (n = 23), and 11–16% for house painters (n = 23), while the corresponding time above 90° was 2%, 5% and 5–9%. In that study, they found an exposure-response relationship between work time with arms above 90° and shoulder disorders. Some interventions for hairdressers have been presented previously, on organizational factors (Nassaji et al., 2015), physiotherapy exercise program (Bertozzi et al., 2011) and work technique with existing equipment (Arokoski et al., 1998; Veiersted et al., 2008; Fang, 2010). We have only found one study on changes in design of used equipment, and that is of scissor design (Boyles et al., 2003). No studies of intervention on blow-dryer design has been found. When a professional blow dryer with radical new ergonomic design was developed, the opportunity arose to test the possible effect on the hairdresser's work posture. In a Taiwanese study, blow-drying constituted 16–32% of the hairdressers' active work (Chen et al., 2010). Handheld blow dryers used in hair salons have traditionally had a ‘pistol-like’ design with one air outlet and a handle with control buttons perpendicular on the air outlet. To improve the ergonomics of blow-drying, a Norwegian hairdresser designed a handheld blow dryer where the airflow can switch between two air outlets. These air outlets point in opposite directions and one air outlet function as a handle with control buttons (Fig. 1). The idea is to allow the upper arms of the hairdressers hang freely down

Corresponding author. E-mail addresses: [email protected], [email protected] (M. Wærsted).

https://doi.org/10.1016/j.ergon.2019.102839 Received 18 January 2019; Received in revised form 16 July 2019; Accepted 30 August 2019 0169-8141/ © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/).

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Fig. 2. The professional Parlux1300 blow dryer with traditional “pistol” design used in the laboratory part of the study, for comparison with the blow dryer with the new design. The blow dryer is shown without the removable nozzle.

Fig. 1. The professional blow dryer with new design (www.dualair.com). The hairdresser can alternate the airflow in two directions. The hand holding the blow dryer grips loosely around the lower air outlet, with the fingers serving the touch button panel. The weight of the blow dryer rest on the hand. The intention of the blow dryer design is to allow the hairdresser to blow dry with the upper arm in a resting vertical position.

the amount of time a hairdresser have their upper arms lifted during work. The new blow dryer should be held with a loose grip around the lower air outlet, letting the body of the dryer rest on the hand. The fingers of the hand holding the dryer operate touch buttons to switch direction of the airflow between the two outlets, and to control the speed and the temperature of the airflow. In the hair salons, the blow dryer with the new design was compared to the traditional blow dryers of the participating hairdressers. In the blow-drying of mannequin heads in the laboratory, the new dryer and a Parlux1300 blow dryer (Fig. 2) were compared. Fig. 3 illustrates the main function of the blow dryers, with arrows indicating airflow direction. Both dryers had their main mass (the engine) placed along the handle axis, resulting in minimal offset distance between the centre of mass and handle axis. In part due to the different designs, the blow dryers in this project differed in weight. The research assistant noted approximate weight of all blow dryers used in the salons on the recording days, by following a standardized procedure for weighing the body of the dryers in question on a simple kitchen weight (same kitchen weight used for all measurements). The dryer with the new design had a weight of approximately 700 g, while the traditional dryer used in the laboratory weighed approximately 500 g. The traditional handheld blow dryers used in the hair salons differed considerably in weight. On the recording days giving the data used in this paper, they varied from about 360 g up to about 670 g (median 600 g). To get an idea whether the differences in weight had a major influence on the results from the measurements in the hair salons, we performed additional analyses including only the ten participants using a traditional blow dryer weighing 600 g or more on the recording day in the hair salon.

to a much higher degree during blow-drying. This new dryer design represents, to our knowledge, the first radical attempt to improve professional blow dryer design for these purposes. The aim of the present study was to document upper arm inclination during blow-drying, and to test if the use of the new dryer, influenced this inclination, compared to the situation when the hairdressers used a dryer with traditional design. Our main focus was on the arm holding the blow dryer, as the posture of this arm was the target of the intervention. However, we subjected the other arm to the same analyses, to capture any unexpected effects on this arm by introducing the new blow dryer. Pain reports were followed throughout the study period to check possible changes in pain experience. The protocol gave the hairdressers a two to three months period to get accustomed to the new blow dryer in their daily work in the hair salons before arm inclination was measured during a full workday. Short episodes of blow-drying a mannequin head were also included in the measurements, in order to compare the two blow dryer designs under more standardized conditions. 2. Materials and methods 2.1. Participants Twenty-four right-handed full-time female hairdressers from fourteen ordinary hairdressers' salons in the greater Oslo area participated, with a maximum of three hairdressers from each salon. The included salons had all categories of customers (female, male and children). However, the mix of customers could vary according to location and established customer base. The participants’ median age was 30 years (range 21–56) and they had worked as hairdressers between one and half year and 36 years (median 13 years). Five of the participants chose to withdraw from the project before the recording day 2, leaving 19 participants contributing to the data analyses of this paper.

2.3. Protocol The protocol was a follow-up study with crossover design, where the participants came individually to the laboratory on five occasions spread out in time with approximately two months in between each occasion. On all these days, the participants filled in a web-based questionnaire. The first day served as a baseline where the participants were introduced to the study scheme, had a standardized physical examination of the musculoskeletal system, and was interviewed about health status and work experience. At this first occasion, the participant also tried a prototype of the blow dryer with the new design, which at that point in time still had not been put into production. The participants were informed that a new blow-dryer design was tested, but not specific focus on arm elevation. Upon receiving the blow dryer with the new design, the participant was given a thorough instruction as advised by the company producing the blow dryer, on the principles of the blow dryer and on the recommended work technique. They then blow-dried a wetted

2.2. Blow dryers In 2016, a professional handheld blow dryer (Dual Air, www.dualair.com) with a completely new ergonomic design with two air outlets (Fig. 1) was introduced to the hair salons in Norway. The blow dryer was designed and put into production by an experienced hairdresser in order to give the professional hairdressers a means to reduce the postural strain she and other hairdressers perceived when blow-drying customers’ hair. The intent of the design was to allow the hairdresser to blow-dry without having to elevate the upper arm and thus to reduce 2

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Fig. 3. The left drawing illustrates the new dryer blowing upwards, the middle drawing illustrates the new dryer blowing downwards, and the right drawing illustrates the traditional blow dryer with its forward blow direction. The arrows indicate airflow direction.

mannequin head to become familiar with the principles of the blow dryer. A concise instruction pamphlet from the producer followed the dryer. On the remaining visits to the laboratory, the participants were asked about their experiences with the blow dryer, and the basic instruction was repeated, together with blow-drying the mannequin head. Before the second visit to the laboratory the participants were cluster randomized (by hair salon) into two groups, where the group allocation decided when they got a blow dryer with the new design for use in their daily work in the hair salon, as illustrated in Table 1. The first group was instructed to use the new dryer between day 2 and 3, and then switch back to their traditional dryer between day 3 and 4. The second group followed the opposite scheme (see Table 1). Between day 4 and day 5 both groups were instructed to use the new blow dryer. On days 3 and 4, the participants were fitted with recording equipment (posture and muscle activity, see below) in the laboratory. They were then recorded a full ordinary workday in their hair salons. On these days, the participants met at the laboratory approximately 1.5–2 h before the start of their workday. Thus, we selected workdays where the participants were scheduled to start work at 10am or later, but the workdays where not shortened due to the recording. The periods in between the recording days lasted 2–3 months. When working in the hair salons on the recording days the participants used the blow dryer they had used in the preceding weeks, as shown in Table 1. In the laboratory on day 4 when all participants have had several weeks of experience with the new dryer in their hair salons, the participants blow-dried a wetted mannequin head with both types of dryers, in a randomized order before moving to the hair salon. They were instructed to dry the hair of the mannequin just as they would have done with a customer's hair in the salon, including the adjustment of the mannequin head to a preferred height.

participant received a new customer and her different work tasks, both hairdresser specific tasks (blow-dry hair, wash hair, cut hair, and so forth) and other work tasks (cleaning, waiting for a new customer, handling customers in the reception, and so forth). During blow-drying, both in the hair salon and in the laboratory, the assistant kept record on which hand the participant used to hold the dryer. For the analyses in this paper, the activity log was used to select periods with blow-drying and to re-label the measurements of upper arm inclination angle and the upper trapezius EMG from “right side”/“left side” to the “side holding the blow dryer”/“side not holding the blow dryer”. If the participant changed hands for holding the dryer, recordings from both left and right sides thus contributed to the results for the side of the hand holding the blow dryer, as well as for the side of the hand not holding the blow dryer. In addition we performed analyses to get an idea on possible effect of low accuracy of this activity log by only including periods of blow-drying (with the same hand) lasting at least 20 s, as any inaccuracy in the recording of start and stop times of blow-drying (or change of hand) would have most impact on the estimates from very short periods of blow-drying. In addition to total time using the blow dryer in the hair salons, we selected continuous periods longer than 5 min using the dryer with the extra criterion that the participant should not change which hand she held the dryer. Seventeen participants had at least one period fulfilling these criteria with both types of blow dryers. These periods were used to see whether the conclusions of our main analyses would change when shorter periods were omitted. The rationale for this additional analysis was an assumption that the position of the upper arm during longer periods of continuous blow-drying with the same hand may be most important for potential adverse outcomes like musculoskeletal pain.

2.4. Activity log

2.5. Inclination of the neck and upper arms

The research assistant followed the participants both in the laboratory and in the hair salons and observed their work during the whole workday. Time points for start and end of the participants’ work tasks were recorded in an app (FieldNotes) on an iPhone. The program had pre-programmed buttons allowing the assistant to specify when the

Four triaxial accelerometers with integrated data logger (AX3, Axivity Ltd, Newcastle, UK) were attached to the upper arms (below the insertion of the deltoid tendon), the upper back (at the level of vertebra C7) and the forehead. A sampling rate of 100 Hz was used. The signal was resampled to 20 Hz and filtered using a low-pass, finite-duration

Table 1 Scheme for use of blow dryer in the hair salons and in the laboratory. Day 1 Blow dryer used in the laboratory Blow dryer in hair salon - group 1 Blow dryer in hair salon - group 2

Day 2

2–3 months

Day 3

2–3 months

Day 4

2–3 months

N T

N T

T N

T/N T N

N N

T = Blow dryer with traditional design. N = Blow dryer with new design. Days with recording of arm inclination and trapezius EMG shown in bold letters. 3

Day 5

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impulse response filter with a cutoff frequency of 5.0 Hz (Hansson et al. 2001, 2006). Values for +1 g and −1 g for each axis of each inclinometer were used for calibration. All recordings had satisfying quality. Zero inclination for the upper arms was established at the start of the recording, one arm at a time, by in a seated position tilting the upper body to the side and letting the arm hang down freely with a 1 kg dumbbell in the hand. Zero inclination for the upper back and forehead was established by letting the participant stand upright looking forward to a point fixed at eye height. Head forward inclination angle was calculated by subtracting back inclination angle from the inclination angle of the forehead. These procedures are extensively described elsewhere (Hansson et al., 2006). From the measurements of the upper arm inclination angle the 10th, 50th (median), 90th and 99th percentiles were calculated, as well as the amount of time with the upper arm elevated more than 30°, 60° and 90°.

to use (‘heaviness’). They were asked to rate blow-drying short hair, blow-drying long hair, volume blow-drying, and finally give an overall rating of the two blow dryers. 2.8. Questionnaires and pain reports On all visits to the laboratory, the participants filled in a web-based questionnaire exploring pain experienced during the last four weeks in the following eight body regions: Neck and upper back, lower back, right shoulder, left shoulder, right arm/wrist/hand, left arm/wrist/ hand, and headache. They stated the pain intensity for each region: no pain (0), mild pain (1), moderate pain (2) and severe pain (3). When answering mild, moderate or severe pain, they were also asked to state the number of days (four categories) with pain experienced during the last four weeks: 1–5 days (1), 6–10 days (2), 11–14 days (3) or 15–28 days (4). Multiplying the scores for intensity and duration gave a muscle pain index (score 0–12) for each body region. Both the pain intensity and the pain index were used in the analyses. From the first baseline visit to the laboratory until the last visit (day 5) the participants were asked to use their cell phones daily for answering of a short web-based questionnaire. At an individually agreed time every evening, participants received a text message with a link to the questionnaire. The questionnaire contained questions regarding the number of hours worked and any musculoskeletal complaints from the day. Complaints in seven body regions (the same regions as in the questionnaire above) were rated on an eleven-point scale where ‘0’ meant ‘no pain or complaints’ and ‘10’ meant the ‘worst imaginable level of pain’ in the body region rated. For each body region the mean score from all working days the last three weeks before the recording days were used in the analysis. As many of the participants changed hands holding the blow dryer during the workday, the mean of the pain scores for the left and right side was used in the analyses for shoulder pain and lower arm pain.

2.6. Electromyography (EMG) Surface EMG from the upper trapezius muscles is a frequently used indicator both of mechanical exposure to the neck and shoulder region, and of muscle activity related to mental distress. Upper trapezius EMG was in this study sampled bilaterally with an ambulatory system (Mobi 8, TSMi, Enschede, the Netherlands) using self-adhesive pre-gelled Ag/ AgCl electrodes (Ambu Neuroline 720, Ambu, Ballerup, Denmark) centred 20 mm laterally from the midline between acromion and the spine at the level of vertebra C7. The electrodes had an interactive diameter of 6 mm and a centre-to-centre distance of 20 mm. At the start of the EMG recording, the subject performed standardized maximum voluntary contractions of the upper trapezius muscles, one side at a time, by having the arm abducted 90° in the scapular plane against resistance performed manually by the investigator. This procedure was repeated three times and the highest EMG response (EMGmax) was used as reference in a normalization procedure presenting the EMG data in percentage of the individual maximal voluntary muscle activity (% EMGmax) (Hansson et al., 1997; Veiersted et al., 2007). The EMG signal (sampling rate 1,024 Hz) was band-pass (30–400 Hz) and notch filtered (50 Hz and all harmonics). EMG amplitude was characterised by the root mean square (RMS) value, calculated for epochs of 1/8 s, and the recorded noise level was, in a power sense, subtracted from the RMS value (Hansson et al., 1997). EMGmax was calculated by a moving window mean over four consecutive samples, giving a time base for the EMGmax of 0.5 s. Power spectrum, mean power frequency and an artefact index were, in combination with the raw EMG, used to identify and exclude sequences with movement artefacts and electromagnetic interference (Nordander et al., 2004). For one participant the recording of electromyography (EMG) failed on two recording days (day 1 and day 3). All the other EMG recordings had satisfying quality with none or only a few very short periods excluded due to artefacts. From the EMG measurements five commonly used measures were calculated: 10th percentile (often labelled “static level”), 50th percentile (median), and 90th percentile (often labelled “peak level”), as well as “muscle rest” (fraction of time below 0.5% EMGmax) and “gap frequency” (number of periods with duration > 1/8 s below the level of 0.5% EMGmax per minute).

2.9. Clinical examination The standardized examination of the musculoskeletal system was performed by the first author (MW) and focused on the neck, shoulders, and arms following a scheme extensively described elsewhere (Sluiter et al., 2001). The participants were checked for tension neck syndrome, radiating neck pain, rotator cuff syndrome, lateral or medial epicondylitis, and tendinitis in the lower arm. This examination was repeated on day 5. In addition, the participants were asked about their health status and had their blood pressure measured as a screening to assure that only healthy individuals were included in the study. No potential participants were excluded for health reasons. 2.10. Ethics The participants signed a consent form underscoring that they could withdraw from the study at any point in time without giving any reason. The study is in accordance with the Declaration of Helsinki. The Data Protection Official for Research at the Norwegian Centre for Research Data approved the ethical aspects of the research protocol and the information given to the participants (NSD project 30759).

2.7. Interviews

2.11. Statistics

At baseline the participants were interviewed on their work experience as a hairdresser. At the final visit to the laboratory (day 5) the participants were interviewed on their experiences with the new blow dryer, and they rated both the new dryer and the traditional handheld dryers they used in their hair salon. They were asked to rate the dryers on an eleven-point scale from ‘0’ (not suitable at all) to ‘10’ (very suitable) for three aspects: 1) how efficient the blow dryer was with regard to time use (‘time use’); 2) the function of the blow dryer with regard to the task in question (‘functionality’); 3) how heavy the blow dryer was

The crossover design allowed a matched pair analytical strategy, using paired T-test or Wilcoxon matched pair tests (IBM-SPSS, version 25), depending on the distribution of the data. A two-tailed p-level of 0.05 or less was regarded as statistically significant. In spite of a large number of dependent variables tested, no Bonferroni corrections have been implemented. Thus, it should be noticed that just by chance about one in 20 comparisons could be expected to have a significant finding with equal possibility for either direction of a difference between the 4

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results as for the full analysis, regarding the arm holding the dryer. For the other arm the tendency for more pronounced elevation with the new blow dryer seen in the full analysis were statistically significant for all seven parameters.

two conditions (the use of either a traditional blow dryer or a blow dryer with the new design). 3. Results

3.2. Muscle activity during blow-drying

When scheduled pauses and passive waiting were subtracted, the median duration of active work in the recordings from the hair salons was 5 h (range 1¼ hour – 7 h). The participants used the blow dryer 26 min (median, range 7–62 min). In the laboratory, the participants used 8 min (median, range 5–14 min) to blow-dry the mannequin heads on day 4. The time each participant used when blow-drying the mannequin head did not differ between the two blow dryer designs. All participants were right-handed. However, they differed with respect to which hand they held the dryer during blow-drying. Nine of the nineteen participants used only the right hand, while the other ten participants changed hands for holding the dryer several times during blow-drying. When blow-drying mannequin heads in the laboratory on day 4, ten of the participants used only the right hand. The analysis regarding arm postures and muscle activity during blow-drying presents data separately for the arm holding the blow dryer and the arm not holding the dryer. Thus, the results for the arm holding the dryer will include data from both right and left side for the participants that changed hands during blow-drying, and the same will be the case for the other arm.

There were no statistically differences in nine of the ten measures of trapezius muscle activity while blow-drying in the hair salons (Table 4). However, when blow-drying on mannequin heads, both upper trapezius muscles had significantly less activity when using the dryer with new design (Table 5). The results of the additional analysis only including the ten participants that used a traditional blow dryer on the recording day weighing 600 g or more did not differ from the full analysis. 3.3. Muscle discomfort and pain The participants reported very low levels of discomfort and pain for all five body regions, see Table 6. Only in two out of fifteen comparisons there were a statistically different reporting depending on which blow dryer they had used during those four weeks, with the headache index higher with the traditional blow dryer and the lower arm pain index higher with the new blow dryer. The daily pain reports also showed a tendency towards more pain in the lower arms when using the dryer with the new design. The clinical examination at baseline and at the last recording day showed few clinical signs of musculoskeletal disorders and there was no pattern in the changes from before until after the study period.

3.1. Postures during blow-drying The arm holding the blow dryer was less elevated with the new blow dryer. Of the seven different measures shown in Table 2, this finding was significant for uppermost percentiles of angle level and for time above 60° and 90° elevation. For the arm not holding the dryer, the results were opposite with four of the seven measures showing significantly higher inclination angles with the new blow dryer. However, for this arm the uppermost percentiles and time above 90° was not significantly influenced. The blow-drying of mannequin heads in the laboratory showed very similar results for the arm holding the blow dryer, but less clear results for the other arm (Table 3). The head forward inclination angle was not influenced by which blow dryer the participants used neither in the hair salons nor in the blow-drying of mannequin heads in the laboratory (data not shown). The additional analyses only including periods of blow-drying (with the same hand) lasting at least 20 s, did not yield different results from the full analysis. The analyses from the hair salons including only continuous periods longer than 5 min using the dryer with the same hand showed similar

3.4. The participants’ evaluation of the blow dryers When the participants rated the blow dryers on the last recording day, thirteen of them rated their traditional dryer as more suitable than the dryer with the new design for all three aspects (‘time use’, ‘functionality’, and ‘heaviness’). Three participants gave consistently best rating to the new dryer. The rating from the last three participants varied with respect to the different aspects they were asked to rate. Table 7 gives more details on the ratings, showing that the difference in rating was most pronounced for the ‘heaviness’ aspect, and least pronounced for the task of blow-drying long hair. When the participants were interviewed on their experiences with the new blow dryer, all participants, with one exception, had at least one positive comment. However, in weighing perceived positive and negative aspects, the majority preferred their traditional blow dryer. Among positive

Table 2 Inclination of the upper arm while blow-drying during a full workday in the salons (N = 19). Traditional blow dryer

The arm holding the blow dryer 10th percentile (°) 50th percentile (°) 90th percentile (°) 99th percentile (°) Time above 30° (%) Time above 60° (%) Time above 90° (%) The other arm 10th percentile (°) 50th percentile (°) 90th percentile (°) 99th percentile (°) Time above 30° (%) Time above 60° (%) Time above 90° (%) 1

Blow dryer with new design

Mean (SD)

Range

Mean (SD)

Range

P1

15.1 (4.6) 36.0 (11.4) 73.0 (15.8) 96.2 (13.8) 56.3 (15.3) 21.8 (13.8) 4.8 (7.1)

9.8–23.7 21.5–62.9 46.7–113.0 70.5–126.9 27.3–82.0 3.1–52.4 0.0–31.3

17.3 (4.5) 34.7 (7.5) 59.5 (9.2) 79.6 (9.2) 59.0 (14.6) 12.0 (9.8) 0.5 (0.4)

9.2–25.8 22.5–52.0 46.0–76.6 61.1–89.6 32.4–84.6 1.2–38.0 0.0–1.1

0.007 0.48 < 0.001 < 0.001 0.40 < 0.001 0.015

16.4 (4.1) 39.0 (7.7) 73.0 (12.4) 92.6 (12.1) 63.6 (11.9) 22.4 (11.9) 3.5 (4.4)

10.3–23.8 25.8–53.6 45.3–93.9 71.1–113.1 38.1–81.3 3.6–42.9 0.02–13.7

18.8 (5.3) 43.8 (9.9) 75.0 (12.8) 93.7 (12.3) 69.2 (13.1) 27.2 (14.7) 4.0 (4.2)

7.7–28.0 21.4–65.5 45.6–93.4 69.9–111.9 27.6–87.8 4.3–58.0 0.01–12.2

0.010 0.004 0.36 0.63 0.016 0.010 0.61

Matched pair t-test. 5

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Table 3 Inclination of the upper arm while blow-drying mannequin head (N = 19). Traditional blow dryer

The arm holding the blow dryer 10th percentile (°) 50th percentile (°) 90th percentile (°) 99th percentile (°) Time above 30° (%) Time above 60° (%) Time above 90° (%) The other arm 10th percentile (°) 50th percentile (°) 90th percentile (°) 99th percentile (°) Time above 30° (%) Time above 60° (%) Time above 90° (%)

Blow dryer with new design

Mean (SD)

Range

Mean (SD)

Range

P1

14.7 (3.6) 29.6 (6.7) 58.6 (14.9) 80.4 (12.4) 46.6 (16.0) 11.3 (8.1) 1.2 (2.9)

9.0–22.0 15.2–42.0 38.0–91.2 61.2–105.3 13.5–72.1 1.2–30.0 0.0–10.8

16.6 (4.3) 30.2 (6.3) 48.0 (9.9) 62.2 (9.7) 48.3 (19.6) 4.1 (5.5) 0.01 (0.03)

8.8–24.1 20.4–40.5 32.5–65.9 43.1–82.9 14.1–75.9 0.0–17.9 0.0–0.08

0.018 0.65 0.001 < 0.001 0.64 < 0.001 0.087

15.8 (4.8) 36.0 (11.2) 65.6 (14.9) 84.8 (15.2) 57.0 (18.5) 17.9 (14.4) 1.9 (2.5)

8.3–28.7 18.6–62.2 34.8–88.1 55.3–105.8 15.9–88.3 0.5–52.0 0.0–8.4

16.7 (4.9) 37.6 (10.4) 67.9 (14.8) 84.4 (14.3) 60.0 (16.7) 19.3 (14.5) 2.2 (3.0)

10.4–28.8 19.6–63.8 33.9–87.9 52.9–107.9 15.4–88.4 0.3–52.8 0.0–8.0

0.013 0.15 0.083 0.86 0.071 0.16 0.45

1)

Matched pair t-test.

Table 4 Upper trapezius EMG while blow-drying during a full workday in the salons (N = 18). Traditional blow dryer Mean (SD) The side of the arm holding the blow dryer 2.8 (1.7) 10th percentile (%EMGmax) 50th percentile (%EMGmax) 10.0 (3.0) 19.1 (4.4) 90th percentile (%EMGmax) Muscular rest (% time) 2.0 (3.6) −1 Gap frequency (min ) 3.1 (3.8) The other side 10th percentile (%EMGmax) 2.1 (1.5) 50th percentile (%EMGmax) 8.5 (4.0) 17.7 (5.9) 90th percentile (%EMGmax) Muscular rest (% time) 1.8 (2.6) −1 Gap frequency (min ) 3.6 (4.1)

Blow dryer with new design Range

Mean (SD)

Range

P1

0.3–5.5 5.3–14.9 12.1–27.3 0.0–15.6 0.0–15.0

2.7 (2.0) 10.6 (6.2) 21.5 (9.8) 1.8 (2.5) 3.8 (4.9)

0.5–6.7 2.1–26.3 10.8–50.1 0.0–9.6 0.0–16.4

0.67 0.54 0.14 0.57 0.38

0.5–6.5 1.6–15.6 7.9–29.7 0.01–10.3 0.06–14.1

2.5 (1.5) 9.6 (4.7) 19.1 (6.8) 1.7 (3.0) 3.7 (5.7)

0.5–6.4 1.8–17.7 8.8–32.0 0.01–10.8 0.04–16.5

0.049 0.14 0.21 0.89 0.90

1)

Matched pair t-test.

Table 5 Upper trapezius EMG while blow-drying mannequin head (N = 19). Traditional blow dryer Mean (SD) The side of the arm holding the blow dryer 10th percentile (%EMGmax) 2.8 (2.7) 8.0 (4.6) 50th percentile (%EMGmax) 90th percentile (%EMGmax) 15.6 (6.7) Muscular rest (% time) 5.5 (10.2) Gap frequency (min−1) 7.8 (11.7) The other side 10th percentile (%EMGmax) 2.5 (2.2) 50th percentile (%EMGmax) 7.9 (5.4) 16.1 (7.6) 90th percentile (%EMGmax) Muscular rest (% time) 4.2 (6.7) Gap frequency (min−1) 8.8 (13.8)

Blow dryer with new design Range

Mean (SD)

Range

P1

0.3–7.7 0.6–16.4 3.4–28.9 0.0–41.9 0.0–46.4

2.1 (1.8) 6.7 (4.6) 13.8 (7.1) 3.9 (5.9) 7.8 (10.4)

0.3–5.6 0.9–16.9 1.7–29.4 0.0–20.5 0.0–35.3

0.041 0.008 0.011 0.28 0.98

0.3–7.7 0.7–18.5 1.7–31.1 0.0–25.5 0.0–55.6

2.1 (1.9) 7.3 (4.9) 15.4 (7.4) 4.0 (6.7) 8.5 (13.8)

0.3–7.6 0.7–17.0 1.5–28.6 0.0–26.1 0.0–53.4

0.11 0.054 0.088 0.55 0.65

1)

Matched pair t-test.

comments many emphasized that the blow dryer made them lower the arm, that it was practical to have a bidirectional air flow, that the blow dryer was powerful (dries fast), and that the blow dryer was very suitable for blow-drying long hair and for volume blow-drying. Among negative comments many felt the blow dryer was heavy and a bit noisy. Nearly all participants found it difficult to adapt their blow-drying technique to the design of the new dryer.

4. Discussion The new professional handheld blow dryer tested in this project, was designed to reduce the amount of time the hairdresser has the upper arm in an elevated position. Even if the median upper arm inclination angle was not significantly changed, the results match this intent by showing that the 90th and 99th percentiles of upper arm

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Table 6 Discomfort/pain in neck, shoulders and lower arms. N

Daily report on pain/discomforta Headache intensity (0–10) Neck pain intensity (0–10) Low back pain intensity (0–10) Shoulder pain intensity (0–10)c Lower arm pain intensity (0–10)c Pain last four weeksb Headache intensity (0–3) Headache index (0–12) Neck pain intensity (0–3) Neck pain index (0–12) Low back pain intensity (0–3) Low back pain index (0–12) Shoulder pain intensity (0–3)c Shoulder pain index (0–12)c Lower arm pain intensity (0–3)c Lower arm pain index (0–12)c a b c d

Traditional blow dryer

Blow dryer with new design

Median (quartiles)

Median (quartiles)

Pd

19 19 19 19 19

0 (0–0.3) 0.1 (0–0.5) 0.1 (0–0.8) 0.0 (0–0.3) 0.0 (0–0.1)

0 (0–0.5) 0.2 (0–0.6) 0 (0–1.3) 0.2 (0–0.5) 0.04 (0–0.4)

0.69 0.88 0.10 0.27 0.046

19 19 19 19 19 19 18 18 18 18

1 1 0 0 0 0 0 0 0 0

1 1 0 0 0 0 0 0 0 0

0.10 0.020 1.0 0.72 0.16 0.16 1.0 0.91 0.41 0.064

(0–1) (0–2) (0–1) (0–1) (0–1) (0–1) (0–0.5) (0–0.5) (0–0.5) (0–0.5)

Mean from daily reports last three weeks before recording days 2 and 3. Pain reports in questionnaires filled in at the start of recording days 2 and 3. Mean of pain reports from the right and left side. Wilcoxon matched pair test.

distinguished significantly cases from referents. Svendsen and coworkers (Svendsen et al., 2004) in their study on male machinist, car mechanics and house painters, found a dose-response relationship between work with upper arm elevation and shoulder disorders, with an odds ratio of 1.23 for supraspinatus tendinitis and 1.16 for shoulder pain with disability, for each duration increment of 1% of worktime with upper arm elevated above 90°. The arm inclination angles were decided with objective measures (accelerometers) for four consecutive full working days in a random sample of 72 subjects out of their cohort of 1886 workers. Hanvold and co-workers (Hanvold et al., 2015) followed 15 female hairdressers in their first 2.5 years of working life. At baseline, they had arm elevation measured with accelerometers for a full working day. Prolonged work with upper arm inclination angels above 60° and above 90° were associated with development of shoulder pain. In the present study, the median inclination angle was not statistically different depending on which blow dryer the participants used. However, the more extreme elevation represented by the 90th and 99th percentiles as well as time above 60° and above 90° was significantly reduced when the participants used the blow dryer with the new design. For the arm not holding the blow dryer, the results tended to go in the opposite direction, with less arm elevation when using the traditional blow dryer. This finding was less pronounced, especially for the more extreme elevations where only the time above 60° was significantly different. The focus of this study was on the effects on the arm holding the blow dryer. We do not have any data or hypothesis on why this new design for some subjects should increase the elevation of the arm not holding the dryer. Furthermore, we do not know if this effect is transient or if it is related to an inexpedient work technique with the new blow dryer. The height of the head of the customer (or of the mannequin) in relation to the hairdresser can have an effect on the arm posture. It was in this project not possible to standardize this height, neither between lab and hair salons, nor between recording days in the hair salons. Thus, we do not know to what extent this relationship might have differed between recordings. However, both in the lab and in the hair salons the participants themselves adjusted this height to their preferred level. While the time with pronounced arm elevation was reduced when using the blow dryer with the new design, the activity of the upper trapezius muscle on the same side was only reduced in simulated blowdrying in the laboratory. The deltoid and the suprascapular muscles,

Table 7 Subjective rating of the blow dryers (higher score is more suitable) N = 19.

Overall rating Time usea (0–10) Functionalityb (0–10) Heavinessc (0–10) Blow-drying short hair Time usea (0–10) Functionalityb (0–10) Heavinessc (0–10) Blow-drying long hair Time usea (0–10) Functionalityb (0–10) Heavinessc (0–10) Volume blow-drying Time usea (0–10) Functionalityb (0–10) Heavinessc (0–10) a b c d

(0–1) (0–1) (0–1) (0–1) (0–1) (0–1) (0–0.5) (0–0.5) (0–0.5) (0–0.6)

Traditional blow dryer

Blow dryer with new design

Mean (SD)

Range

Mean (SD)

Range

Pd

7.8 (1.4) 8.0 (1.3) 7.8 (1.5)

5–10 5–10 5–10

6.3 (2.5) 5.4 (2.5) 5.0 (3.2)

1–10 1–10 0–10

0.052 0.001 0.004

7.6 (1.8) 8.1 (1.2) 8.2 (1.4)

2–10 6–10 5–10

6.6 (2.1) 5.3 (2.6) 4.3 (2.8)

2–10 1–10 0–10

0.22 0.001 < 0.001

7.0 (2.1) 7.4 (1.5) 7.8 (1.8)

0–10 4–10 3–10

6.9 (2.5) 6.8 (2.5) 5.6 (3.0)

1–10 1–10 0–10

0.90 0.42 0.005

7.5 (1.7) 8.0 (1.5) 7.6 (1.8)

3–10 4–10 4–10

6.2 (2.8) 5.3 (2.6) 4.7 (3.0)

0–10 1–10 0–10

0.15 0.004 0.004

The efficiency of the blow dryer with regard to time use. The function of the blow dryer with regard to the task in question. How heavy the blow dryer was to use. Matched pair t-test.

inclination angles, as well as the amount of time with pronounced arm elevation, on the side holding the dryer, was significantly reduced with the new dryer, both in the hair salons and in the blow-drying of mannequin heads in the laboratory. Thus, the findings indicate that giving the hairdresser the possibility to switch the direction of the airflow without changing arm posture would result in less blow-drying with elevated arms. This new dryer represents, to our knowledge, the first radical attempt to improve the blow dryer design for these purposes. In a case-referent study on shoulder disorders in automobile assembly work, Punnett and co-workers (Punnett et al., 2000) videotaped typical work cycles and decided upper arm inclination angles in 79 cases and 125 referents. The upper arm inclination angles were grouped in three bins: below 45°, between 45° and 90°, and above 90°. Only time with the upper arm inclination angle above 90° during the work cycles 7

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and not the upper trapezius muscle, are the main muscles for elevating the upper arm. The upper trapezius stabilizes the shoulder and to a lesser degree contributes to an elevation of the shoulder girdle. Besides, research into stress-related muscle activation have shown that the upper trapezius muscles are among the more reactive muscles to mental load (Wærsted and Westgaard, 1996). In the hair salon, the participants have several challenges that may trigger activity in the upper trapezius unrelated to arm elevation, such as time pressure, customer demands, and so forth. This may explain the different pattern of trapezius muscle activity in the laboratory and in the hair salons. This project included both field recordings in hair salons during ordinary workdays, as well as recordings from an experimental setup in the laboratory. The participants got a standard instruction on work technique when they received the new blow dryer and had a 2–3 months period using this blow dryer in their daily work, before being recorded a full workday. Thus, the field recordings gave us the better idea of the influence on upper arm posture and trapezius muscle activity when a group of experienced hairdressers start to use this new blow dryer in their hair salons. However, we had little control of the way they used the blow dryer in this 2–3 months period. In the laboratory we could standardize the work task, let the participants use the same traditional blow dryer for comparison with the blow dryer with new design, and make sure that the participants used the new blow dryer according to the advised principles. In these respects, we had far better control in the laboratory of factors that might influence the results, compared to the situation in the hair salons. However, blowdrying a mannequin head in a laboratory set-up is rather different from real work life. Besides the Parlux1300 might differ to a greater or lesser extent from the traditional blow dryers the participants used in their hair salons. The focus of this study was on upper arm posture during blow-drying, and it strengthens the results that there was a high agreement between the findings in the hair salons and in the laboratory. The design of the new blow dryer was radically different from that of the traditional handheld blow dryers, as can be seen in Fig. 1, demanding a very different blow-drying technique. The results of this project showed that this new design made the participants reduce their time with the upper arm in pronounced elevation. However, the research assistant following the participants in the hair salons on the recording days, observed that some of the participants to a greater or lesser extent used the blow-drying technique they were used to with their traditional dryer, when using the new dryer. Used in this manner, the new blow dryer can be expected to increase the workload, rather than reduce it, as the new dryer was among the heaviest blow dryers and had a design not practical for a traditional way of blow-drying. In the laboratory, the participants were instructed carefully on the principles of the new blow dryer and observed for correct technique when blow-drying the mannequin head. We do not know to what extent the participants' way of using the new dryer in the hair salons in the 2–3 month period before the recording day departed from the intended work technique. Further, we might expect that being unfamiliar with the technique needed to use the new dryer in an optimal way, made some of the participants work in a more tense manner, even if they held the blow dryer as intended. These factors may explain why some participants reported more complaints, even if still on a low level, from the lower arm holding the new blow dryer, and that we found no difference in the reporting of complaints from the shoulder/neck region. The focus of this project has been on the upper arm posture and shoulder load in blow-drying. The lower arm posture has not been studied, so we do not know whether the new design can have some unintended effects on the load on the lower arm and wrist during blow-drying. Besides, both the number of participants in this project was rather small and the followup time rather short when it comes to evaluating the effect on pain and discomfort. Furthermore, blow-drying constituted in this sample a far smaller proportion of active hairdressing work, than we expected based on earlier studies on hairdressers. Thus, it might be of interest to look into the effect of blow dryer design on the hairdressers’ experiences on a

later point in time, when those using the new dryer have acquired a better work technique, the number of users has increased and the blow dryer has been used over a longer time period. A big majority of hairdressers in this study found it difficult to adapt to the new dryer, and preferred the traditional dryer when rating the blow dryers at the end of the study. Only three out of nineteen participants gave their best ratings to the blow dryer with the new design. However, it is valuable to be able to choose between professional tools with different designs in order suit individual needs and preferences. The participants in this project were among the first to start using the new dryer and they received the standard instruction at the time. At a later point in time, the producer of the new blow dryer have started to put more emphasis on instruction with videos and individual training based on similar experiences with other users (DualAir, personal communication, December 2018). We cannot know whether the participants’ preferences at the end of this study had been different if this more intensive instruction for new users had been offered when this project started. The role of senior hairdresser teachers in continuing vocational training may also be important (Aalto-Korte et al., 2016). However, changing work technique is in any case demanding. Possibly our sample of hairdressers did not have enough motivation to do the changes needed to get the better effect of the new design. They were curious and interested in testing a new design, but probably did not see the point in changing well-established elements of their work technique. In a rehabilitation program for hairdressers with musculoskeletal symptoms one measure was to instruct the hairdressers to hold around the air outlet of their (traditional) blow dryer, instead of holding the blow dryer in the conventional way, in order to reduce arm elevation during blow-drying (Arokoski et al., 1998; Nevala-Puranen et al., 1998). This blow-drying technique have some resemblance with the work technique of the new blow dryer when the air flows through the lower air outlet. Indeed, some hairdressers with shoulder symptoms that have tried the new blow dryer have experienced a relief of their musculoskeletal problems (DualAir, personal communication, December 2018). However, this possible use was not part of the present study, where the participants had low levels of musculoskeletal symptoms and were not in need of rehabilitation. The new blow dryer was introduced to the market in Norway in 2016 and it is too early to conclude to what extent professional handheld blow dryers with this new design will be used in the hair salons. Some Norwegian schools for hairdressers have already included training with this new dryer in their curriculum in order to give future hairdressers experience with different types of blow dryers (DualAir, personal communication, December 2018). Possibly, it could be a good idea that blow dryers with different designs are available in the hair salons, to give the hairdressers the possibility to choose the dryer they prefer for any given blow-drying task. 5. Conclusions This study showed that the time with upper arm inclination angle above 60° during blow-drying was reduced when the participants used the new handheld blow dryer. Trapezius muscle activity was reduced when using the new blow dryer, but only in the laboratory setting. After the study period, a majority of the participants preferred to continue with the traditional blow dryer they were used to. Conflicts of interests None. Funding This work was supported by the Confederation of Norwegian Enterprises (NHO) under Grant S-2825. This funding source and the 8

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companies providing equipment for the study had no influence on study design, analysis or interpretation of the data, writing of the article, or decision on submission.

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Acknowledgements We will thank the participating hairdressers and their hair salons for their positive attitudes and their contributing time and resources to the project. Thanks to the companies Cutrin, Tendenz and DualAir for supplying hairdressing equipment, mannequin heads with stands and the blow dryers needed in the laboratory setup and DualAir for giving each participant a blow dryer with new design for use in the hair salon. We thank Jon Husem Marthinsen for skilful assistance during data collection, and Shahrooz Elka and Rune Madsen at the National Institute of Occupational Health in Oslo for handling the web-based systems for answering the questionnaires at the recording days and daily through their smartphones respectively. We also thank Gert-Åke Hansson, formerly at the Division of Occupational and Environmental Medicine, Department of Laboratory Medicine, Lund University, for technical support and important discussions at the outset of this study. References Aalto-Korte, K., Kurimo, R., Laitinen, J., Pesonen, M., Takala, E.P., Poutanen, M.A., 2016. 'Continuing Vocational Training for Teachers in Beauty and Hair Care - Teachers Act as Active Developers of Their Work and Engage in Transferring Godd Practices to Their Students ICERI2016. Seville, Spain, pp. 2386–2394. Arokoski, J.P., Nevala-Puranen, N., Danner, R., Halonen, M., Tikkanen, R., 1998. Occupationally oriented medical rehabilitation and hairdressers' work techniques–A one-and-a-half-year follow-up. Int. J. Occup. Saf. Ergon. 4 (1), 43–56. Bertozzi, L., Capra, F., Barducci, C., Pillastrini, P., 2011. Effect of a physiotherapy program in the management of musculoskeletal disorders in hairdressers: a randomized controlled trial. Italian J. Physiother. 1 (3), 73–79. Bodin, J., Ha, C., Petit Le Manac'h, A., Sérazin, C., Descatha, A., Leclerc, A., Goldberg, M., Roquelaure, Y., 2012. Risk factors for incidence of rotator cuff syndrome in a large working population. Scand. J. Work Environ. Health 38 (5), 436–446. https://doi. org/10.5271/sjweh.3285. Boyles, J.L., Yearout, R.D., Rys, M.J., 2003. Ergonomic scissors for hairdressing. Int. J. Ind. Ergon. 32 (3), 199–207. Bradshaw, L., Harris-Roberts, J., Bowen, J., Rahman, S., Fishwick, D., 2011. Self-reported work-related symptoms in hairdressers. Occup. Med. (Lond.) 61 (5), 328–334. https://doi.org/10.1093/occmed/kqr089. kqr089 [pii]. Chen, H.C., Chang, C.M., Liu, Y.P., Chen, C.Y., 2010. Ergonomic risk factors for the wrists of hairdressers. Appl. Ergon. 41 (1), 98–105. Cruz, J., Dias-Teixeira, M., 2016. 'Work-related musculoskeletal disorders among the hairdressers: a pilot study. In: Goonetilleke, R., Karwowski, W. (Eds.), Advances in Physical Ergonomics and Human Factors. Springer International Publishing), Cham, pp. 133–140. Fang, H.L., 2010. An Investigation into the Solutions for Work-Related Musculoskeletal Disorders in the Hairdressing Industry. PhD Thesis. De Montfort University. Hansson, G.Å., Arvidsson, I., Ohlsson, K., Nordander, C., Mathiassen, S.E., Skerfving, S.,

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