Occupational injuries, daily workload, and tness levels among tness and swimming instructors.

Background. Fitness (FI) and swimming instructor (SI) are two different type of trainers that are usually employed in tness centers and their profession is highly physically demanding because they have to practice while teaching. To date, data on occupational disorders in FI are limited and there is no information about SI. Therefore, the primary outcome of this study was an exploratory analysis of occupational disorders experienced by FI and SI employed in various tness centers through a self-reported questionnaire, to provide rst data on its prevalence. The secondary outcome was to assess tness levels, workloads and perceived exertion during a typical working day of SI and FI in order to explore the possible factors associated with occupational disorders in these professional activities. Methods. An online cross-sectional survey addressing physical data, frequency, duration and time of class participation and self-reported occupational disorders was conducted among 435 subjects (FI=254; SI=179). Subsequently, 97 subjects (FI=57; SI=42), were enrolled to investigate physical tness by maximal oxygen consumption ( O2max), and daily workload by heart rate (HR) and rating of perceived exertion (RPE). differences between statistical differences instructor type in signicantly higher


Background
The tness industry is booming with the last 10 years showing a rapid increase in tness club members and employees with almost 750.000 tness employees in Europe alone [1]. In particular the tness industry is considered to include both tness and/or swimming pool centers. In tness centers costumers can nd lots of equipment for cardio and weight training or group tness classes. In swimming pool centers costumers can nd different types of swimming classes as well as water aerobics courses. Fitness (FI) and swimming instructors (SI) are therefore two different type of trainers that are usually employed in these centers. FI generally lead, instruct and motivate individuals or groups in exercise activities, including cardiovascular exercises, strength training and stretching. Typically, FI works with individual clients designing, explaining and demonstrating various exercises and routines, or teach group classes in which organize and lead tness classes lasted 30-90 minutes. In these classes, instructors may set the music and choreograph in exercise sequence, using also speci c exercise equipment (e.g. stationary bicycles, weights, etc.). SI generally help people learn to swim, improve their swimming skills and to exercise in water. Moreover, they are also specialized to teach during water aerobics classes in which they perform aerobic exercises with water immersed participants. These classes focus on aerobic endurance creating an enjoyable atmosphere with music.
According to this, FI and SI profession is highly physically demanding. In fact, most of the time they have to practice while teaching and they may work nights, weekend, or holydays or have to travel to different gyms or to clients' home to teach classes or to conduct personal training sessions. Despite the numerous health related advantages of physical activity and exercise, the risk of occupational disorders among FI and SI is poorly addressed. One of the rst studies about this topic found that aerobic dance instructors during 29.924 hours of practice have 84 time loss injuries for a rate of 0.26 [2]. Moreover, Rothenberger et al. [3] found in a sample of 726 aerobic dancers that 49% of the subjects reported a history of at least one injury related to aerobic dancing. Most of the injuries were to the calf (24.5%), lower back (12.9%), and ankle (12.2%). Among those subjects injured, 23% reportedly saw a physician because of their injury. The frequency with which subjects exercised was associated with a history of injury. Subjects who exercised fewer than four times per week reported fewer injuries (43%) than those who exercised four times per week (60%) or more (66%). Another study, found prevalence numbers among aerobics instructors as high as 77% with the most frequent injury location being leg, foot/ankle and knee [4]. Romaine et al. [5] found that 31% of cardio kickboxing instructors had experiences injuries relates to such classes and reported back, knee, hip and shoulder as the most frequent injury locations. Malliou et al. [6] reported that 73.5% of step aerobics instructors had chronic lower extremity injuries. Solfrid Bratland-Sanda [7] reported a high prevalence of instruction-related injuries and musculoskeletal pain among the group tness instructors.
In addition, FI and SI rely on their voices in a similar way that performers, classroom teachers, salespeople, and others in vocally demanding professions do [8]. In fact, FI and SI reported voice di culties that appear to be the result of an interaction between both environmental and physiological stress placed on the voice when that are encountered when speaking and vigorous exercise occur simultaneously [9]. For this reason, FI and SI voice is an essential professional asset used not only to provide education and direction, but also to motivate and encourage class participants to persevere [10].
The vocal effectiveness of the instructor has a direct in uence on the satisfaction of clients and keeps them motivated to return, and the amount and type of verbal motivation required is often driven by tness genre [8]. There are also several factors that can strain the use of vocals because instructors vocalize with music and other noise sources and teach in acoustically poor spaces [10]. To this regard, Heidel & Torgerson [8] found that aerobics instructors generally experienced more hoarseness and episodes of voice loss during and after instructing and a signi cantly higher prevalence of nodules. In the same way, Long et al. [10], observed that aerobics instructors experienced partial or complete voice loss during and after instructing, as well as increased episodes of voice loss, hoarseness, and sore throat unrelated to illness since they began instructing. Finally, Rumbach [9] identi ed that group tness instructors are susceptible to a number of voice disorders (e.g. laryngeal pathology, vocal strain, dysphonia etc.) that impact their social and professional lives.
Since studies on the occupational disorders experienced by FI are limited and there are no information about SI, the primary outcome of this study was to investigate the prevalence of occupational disorders experienced by FI and SI employed in various tness center companies through a self-reported questionnaire. In addition, the secondary outcome was to assess tness levels, workloads and perceived exertion during a typical working day of SI and FI in order to explore the possible factors associated with occupational disorders in these work activities.

Study design
In order to assess the prevalence of occupational disorders experienced by FI and SI, a retrospective cross-sectional self-reported observational study was conducted. Subsequently, in order to investigate physical tness and daily workload during a typical working day in FI and SI a prospective cross-sectional observational study was performed.

Participant screening
Participants were recruited from various tness centers companies (Get Fit, 20 Hours, Virgin Active). These companies employed both FI (e.g. dance aerobics, step aerobics, spinning, pilates, yoga, low back pain exercise classes, strength training, boxing/kickboxing) and SI (e.g. water aerobics, swimming courses, mother/baby swimming courses). The inclusion criteria were being a FI or SI instructor and teaching a minimum of one class a week. The exclusion criterion was being unable to ll out the questionnaire. Potential participants e-mail addresses were provided by the head of each center. The responders were contacted by email in which they were fully informed about study procedures, bene ts and risks associated with participation. Written informed consent was e-mailed and participant have to sand it back signed. At this point the online survey was e-mailed to the participant who agreed to participate and met above inclusion and exclusion criteria. Participant who agreed also to participate to the second part of the study were phone called in order to organize laboratory testing and daily workload monitoring.

The online survey
The on line survey was created according to the guidelines provided by Artino et al. [11]. Subjects were requested to complete an online survey during a 2 weeks period. The survey requested information regarding personal physical data, frequency, duration and time (early morning, morning, afternoon, or evening) of class participation. For the purposes of this study, all self-reported occupational disorders related to their work during their entire career were asked by answering the following question: "Have you experienced any occupational disorder as FI or SI during your career?" [7]. If positive response, participants have to specify each injury, type of injury (acute/overuse), in accordance with the de nitions provided by the consensus statement regarding disorder registration [12]. Only those participants who saw a physician for their disorders were asked to report a diagnosis. Participants who did not see a physician were asked only to report the location of the disorder. The extent of the disorder was examined through contingency questions regarding the limitation that the injury placed on activity. The survey took 20-25 minutes to complete.

Physical Fitness Assessment
Participants' physical tness was assessed by maximal oxygen consumption assessment ( O 2max ).
Oxygen consumption ( O 2 ), carbon dioxide production ( CO 2 ), and pulmonary ventilation ( E) were measured using a metabolic device on a breath-by-breath basis (Quarkb 2 Cosmed, Rome, Italy) during a graded ramp cycle ergometer test (Monark Ergomedic mod. 839E, Monark, Vansbro, Sweden). All tests were carried out in a well-ventilated laboratory at a temperature of 20-22°C under standardized constant ambient conditions (i.e. a temperature of 22±2°C and humidity of <70%). The protocol consisted of 3 minutes at 50W/min (warm up and familiarization), followed by an increase of 20W every minute until exhaustion. Achievement of O 2max was considered as the attainment of at least two of the following criteria: 1) a plateau in O 2 levels despite increasing speed; 2) a respiratory exchange ratio above 1.1; and 3) a HR of ±10 bpm of age-predicted maximal HR (i.e. 220 -age) [14]. Heart Rate (HR) was recorded during the entire test using a HR monitor (Polar RS800, Polar Electro 2011, Kempele, Finland). Maximal HR at exhaustion was consider as HR max .

Daily Workload Monitoring
Each participant was equipped with a HR monitor (Polar RS800, Polar Electro 2011, Kempele, Finland) and instructed to wear it during their typical workday for one week. In particular, FI and SI were instructed to wear it before the start of their classes and to remove it at the end of the last lesson of the day. For the subsequent analysis, the central 3 hours of this workday has been considered. HR recordings were expressed in the percentage of the maximum value (%HR max ) reached during the maximal oxygen consumption assessment. All the HRs obtained were then compared to the American College of Sports Medicine recommendations [16] for the development of aerobic tness, which de ne the relationship between work HR ranges and work intensity. Participants were asked to continue their normal daily working routine and to maintain their usual diets during the monitoring period.

Rating of Perceived Exertion Assessment
The Borg CR100 scale [14] was selected to rate per perceived exertion of a typical lesson. A verbalanchored was provided to the participants who were instructed to use it 30-min after the end of the last lesson of their working day. Each participant was familiarized with the Borg CR100 scale, including anchoring procedures.

Statistical Analysis
Respondents with missing data were excluded from the analysis. Descriptive statistics (mean ± standard deviation, m ± SD) for the outcome measures were calculated. The normality of the distribution was checked using graphical measures and the Kolmogorov-Smirnov test. Since all anthropometric variables were normally distributed, differences between male and female FI and SI were checked using an unpaired Student's t-test. A Chi-square test was used to compare the questionnaire's variables of educational level, professional information, and job characteristics between FI and SI groups. Differences between FI and SI were studied using the Student's paired t-test when analyzing the perceived exertion after the maximally fatiguing workday, the perceived exertion 30 minutes after the end of their lessons, and the perceived exertion and fatigue upon waking up in the morning. Intra-and intergroup differences (gender ´ instructor type) between in daily workload for FI and SI for O 2max , HR mean , and HR max were checked using two-way analysis of variance (ANOVA) with Bonferroni's multiple comparisons test. The level of statistical signi cance was set at p<0.05. Statistical analysis was performed using the software STATISTICA (version 7.1, StatSoft, Tulsa, OK, USA).

Participants Screening Results
Four-hundred and seventy two participants were invited to complete the on-line survey. Thirty-seven participants did not filled correctly the survey and they were excluded from the analysis. Therefore, 435 instructors were included in the study. Consequently, the response rate was 92.2%. Ninety-seven subjects (57 FI and 42 SI) agreed to also participate in the secondary phase of the study and were tested in order to evaluate fitness level, workload monitoring and perceived exertion of a typical working day (Figure 1). *** Figure 1 near here*** Online Survey Results Table 1 shows participants' demographic characteristics. The subjects in each group were similar in age, height, body mass and body mass index (BMI). Moreover, the number of years spent in their profession was >10 years in only a small percentage of both work groups and the number of weekly work hours was <10 hours in more than half of all FI and between 10 and 30 weekly hours in SI. Overall, a total of 621 musculoskeletal disorders and 521 of other disorders were included in the study with 157 and 155 participants that experienced 2 or more injuries for during their career respectively. Figure 2 illustrates the prevalence of occupational disorders that occurred during the FI and SI entire career, divided into musculoskeletal and other disorders. The percentages of ankle, knee, and wrist sprains, shoulder dislocations, contusions, muscle pulls and contractures, lower back pain, and articular pain were significantly higher in the FI group (p=0.032) versus the SI group. Non-musculoskeletal diseases such as bronchitis, sore throat/aphonia, and headache were significantly more common in the FI group (p=0.014) whereas warts and upper respiratory tract infections were more frequent in the SI group (p=0.025).
*** Figure 2 near here***  Table 2 shows average heart rate (HR mean ) and the ratio between HR mean and HR max (HR mean /HR max ), during 3 hors of the daily workload monitoring. Two-way ANOVA with

Physical Fitness Results
Bonferroni's multiple comparisons test did not show any interaction and statistical differences between instructor type in HR mean and HR mean /HR max . No significant main effect between male SI and FI was found. However, female SI displayed significantly higher HR mean and HR mean /HR max (p=0.018, p=0.022, respectively) than female FI.

Rating of Perceived Exertion Results
The perceived level of fatigue after a typical workday was 72.3±16.2 AU (i.e., arbitrary units in the CR100 scale, a point-scale up to 100 with 100 being the maximum possible level of fatigue) [14] in FI and 72.0±18.0 AU in SI, with no significant differences between the groups. Figure 3 shows the perceived physical fatigue of a typical lesson conducted by FI and SI. About 50% of the SI group and 60% of the FI group reported feeling that their typical lesson was physically "hard", with no significant differences Exercise test between groups. A significantly higher percentage of SI participants described the physical exertion of their lesson as "very hard" (p=0.042 between groups, x 2 test for percentages). *** Figure 3 near here***

Discussion
To the best of our knowledge, the present study is one of the rst that investigated the prevalence of occupational disorders among FI and SI during their career. In particular, we observed that FI had a higher prevalence of instruction related musculoskeletal occupational disorders, whereas SI experienced more acute and chronic voice disorders. Moreover, since FI and SI have to cope with physical and psychomental we provide objective data on their physical tness level and workload during a typical working day.
Regarding musculoskeletal disorders, we observed that muscle tightness (i.e. a shortening of a muscle), with ankle, knee and wrist sprains, shoulder dislocation, contusions, low back pain, and articular pain were very common in FI. Our results are in line with previous ndings among FI [3-5, 7, 15]. Hickey & Hager [15], showed that the most common chronic injuries in aerobic dance instructors were tendinitis, repetitive strain injury, patello-femoral diseases, and medial tibial syndromes, followed by ankles sprain and low-back pain as suggested by Rothenberger et al. [3]. Also, du Toit et al [4] and Bratland-Sanda et al. [7] reported that the lower limbs extremity injuries were very common with the ankle (32.8%) and the knee (20%) as the most common site of injury. Generally, these types of injuries are considered classi ed as chronic injuries, resulting from repetitive force applied to a one tissue, joint, or ligament. To this regard, Bratland-Sanda [7] stated that the greater risk of lower limb musculoskeletal disorders in FI is related with the monotonous exercise modality, which is a primary risk factor for overuse injuries. In addition, Shol & Bowling [16] reported high-intensity training classes, unsuitable oors, shoe type, high number of workouts per day, di cult choreography, and insu cient warm-up are among the factors that may contribute to a higher lower limbs occupational disorders. Finally, Sharff-Olson [17] indicated that also the working weekly classes were detected as one of the variables associated with musculoskeletal disorders. In fact, 4 aerobic dance sessions per week increased the injury percentage from 43% to 66% compared to subjects who exercised 3 times per week or less [17]. On the contrary we found that SI had a less prevalence of musculoskeletal occupational disorders. This was not unexpected because SI work is largely standing (e.g. classic swim classes) or anti-gravitational (e.g. during water immersed aerobic classes).
With regard to the other occupational disorders the present investigation found that both FI and SI are at higher risk of developing both acute and chronic voice di culties associated with the development of sore throat, aphonia and bronchitis. These results corroborate previous research, which found that 58% and 12% of group tness instructors experience hoarseness and voice loss immediately following classes [17]. It seems reasonable to associate these infections with the typical demands of the job that require loud verbal instructions while performing exercise making the control of breathing and air ow movement more stressful. In fact, it has been demonstrated that the interaction between both environmental and physiological stress leads FI and SI to assume a hyper functional behavior that could also be worsen by postural misalignement, breathing patterns, work environment and therefore the adoption of compensatory voicing behaviours [18]. This has been observed especially in young and inexperienced instructors, who can also develop voice overuse and laryngeal diseases in the long run [19]. Another incidental factor may be the poor air quality (e.g. dryness, dust) in the workplace that may cause allergic reactions or sinus infections [20]. Finally, the use of chlorine-based products to sanitize swimming water in SI daily life may affect the respiratory health of SI [21]. Moreover, we observed that SI are at higher risk to develop headache and warts respect FI. Regarding headaches, we hypothesize that the warm temperatures and humidity typical of swimming pool environments may play a role, especially in individuals prone to migraine attacks [22]. For what regard warts it is well known that swimming pools may be a more favorable environment for these types of infections [23].
Regarding the secondary outcome of the study, we are now able to give evidence about physical tness, and daily workload of FI and SI. In particular, we found that FI and SI. O 2max ranged from 47.0±4.0 to 51.9±3.7 ml·kg -1 ·min -1 . In accordance with their age and sex, males FI and SI are between the 70-90 percentiles and female FI and SI are above the 90 percentile of the reference standards for cardiorespiratory tness measured with cardiopulmonary exercise testing using cycle ergometry [24]. We observed that SI and FI did not differed in O 2max during graded maximal test, suggesting that both groups are probably exposed to a similar workload, and thus training, during a workday. Our results are similar with those found in the study of Wanke et al. [25], who studied the work related cardiovascular loads in professional dance teachers. In particular they found that depending on the dance style (e.g. jazz, modern dance, ballet etc.) the average HR load during the lessons ranged between 56.7±7.4% and 63.6±9.8% of the individual HR max . Interestingly, among women we found a signi cant difference about HR mean during a typical working day. To this regard, we could speculate that it might be possible that women are more involved in Aqua Gym or activities that include an active physical participation with respect to men that maybe are more devoted to swimming instruction or training which doesn't include an active involvement.
This study had some limitations. Because of the paucity of research in this area, the rst part of this study was designed as a cross sectional and exploratory. Although this design is less expensive and can be performed in a shorter period of time, some confounding factors such as history of injuries and work habits prior to data collections cannot be controlled. Therefore, antecedent-consequent relationship, as well as occupational disorders and relative risk, cannot be established through this design. Second, it was not possible to perform analysis on differences between respondents and non-respondents. A possible selection bias was that the prevalence of injuries and musculoskeletal pain might be higher among the respondents compared with the non-respondents, thus affecting the results and the external validity of the study. Third, self-reporting of injuries and musculoskeletal pain is also a limitation: we could not ask any of the subject for the medical record. In addition, the self-reporting method makes impossible to verify also the right location and type of the injury. Therefore, no injury severity score was applied.
However, it should be emphasized that this was only a preliminary and descriptive investigation; nevertheless, the results obtained are scarcely available in the literature and can highlight an aspect relating to these poorly protected self-employed workers.

Conclusions
In conclusion, a high prevalence of instruction-related musculoskeletal, occupational disorders and vocal pathologies was observed during FI and SI career. These disorders are probably a consequence of their physically demanding work activities and especially for SI of the work environment. Therefore, data on FI and SI physical tness and daily workload monitoring will provide useful information in order to better focus and design future studies. Moreover, this information will help to set up guidelines regarding maximum weekly teaching load in these workers. Ethics approval and consent to participate

Declarations
The study protocol was approved by the Scienti c and Technical Committee of the ISPESL (Istituto Superiore Prevenzione e Sicurezza sul Lavoro, Italian Ministry of Health, n° B19/DOC/03), and was conduct in adherence to current national laws and regulations governing the use of human subjects (Declaration of Helsinki III). Participants were fully informed of the procedure and signed an informed consent form outlining the study protocol, bene ts, and risks associated with participation.

Figure 2
The gure represents the proportions of individuals of each group (FI and SI), who experienced during their career each speci c musculoskeletal injury or other disorders. Legend: *, p<0.05.