To the best of our knowledge, the present study is one of the first that investigated the prevalence of occupational disorders among FI and SI. In particular, we observed that FI had a higher 2-year prevalence of musculoskeletal occupational disorders, whereas SI experienced more acute and chronic voice disorders. Moreover, since FI and SI have to cope with physical exertion and psychic stress, we provide objective data on their physical fitness level and workload during a typical working day.
Regarding musculoskeletal disorders, we observed that 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 findings 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 classified as overuse 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 floors, shoe type, high number of workouts per day, difficult choreography, and insufficient 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 lower 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 disorders, the present investigation found that both FI and SI are at higher risk of developing both acute and chronic voice difficulties associated with the development of sore throat, aphonia and bronchitis. These results corroborate previous research, which found that 58% and 12% of group fitness 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 airflow 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 compared to 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 fitness, and daily workload of FI and SI. In particular, we found that FI and SI showed the same O2max during graded maximal test and HR during a typical workday. Therefore, the aerobic fitness level was comparable between FI and SI subjects, 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. [24], 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 HRmax. Interestingly, among women we found a significantly higher HRmean during a typical working day in SI with respect to FI. To this regard, we could speculate that it might be possible that women SI are more often involved in Aqua Gym classes or similar training sessions, which require an active physical participation from the instructor, with respect to men SI, who are more likely to be devoted to swimming instruction or training, which doesn’t include an active physical involvement.
This study had some limitations. First, the questionnaire we proposed was custom-made and has not been yet validated nor was checked for internal consistency. After its design, the questionnaire was only submitted to a small group of fitness experts, who evaluated whether the questions effectively captured the topic under investigation. However, the data retrieved with this questionnaire has therefore to be considered as pilot data.
Second, because of the paucity of research in this area, the first 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. Third, 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. Finally, self-reporting of injuries and musculoskeletal pain is also a limitation, since this method makes it impossible to verify the injury location and type by a third party. However, the assessment of physical fitness of FI and SI, as well as daily workload and their perceived exertion, are valuable information for focus and design of future studies. To this regard, it is suggested that future researches consider these factors to conduct stronger longitudinal studies about this topic.