Association between V̇O_2max, handgrip strength, and musculoskeletal pain among construction and health care workers

Musculoskeletal disorders (MSDs) are a major concern in the European population and constitute one of the main reasons for individual complaints and sickness absences [1]. The most prevalent work-related MSDs are low back pain and neck and shoulder pain [2]. The construction and health care sectors have a high prevalence of MSDs [3, 4] and are the sectors with the highest sickness absence rates in Norway [5]. Risk factors for developing work-related MSDs are linked to both mechanical and psychosocial exposures [6]. Construction and health care workers are assumed to have physically demanding jobs and to be exposed to work requiring high energy metabolism and considerable muscle force. A gap between work demand and an individual’s capacities of maximal oxygen uptake and muscular strength may increase the risk of MSDs [7]. To reduce this gap, physical activity worksite programmes have been offered to employees, but there are conflicting results regarding the efficacy of such programmes with respect to musculoskeletal pain [8]. An effect of these interventions presupposes a relationship between individual capacity and musculoskeletal pain or between physical activity and musculoskeletal pain. In the present study we therefore hypothesize a negative association between fitness, strength and MSDs.

A review by the Swedish Work Environment Authority summarized the research on physical activity and physical capacity in relation to work-related MSDs. The majority of the included studies were based on self-reported physical activity. The results were contradictory but indicated that a high level of physical activity may reduce work-related MSDs. Only eight of the included studies described the relationship between physical capacity and musculoskeletal pain, and the results were inconclusive. These inconclusive results revealed a lack of knowledge regarding the association between measured physical capacity and work-related MSDs. According to this review, few studies had separated the results according to profession or gender. The authors suggested that future research should focus on gender and occupational differences [8].

The main aim of this study was to explore the association between individual capacity (maximal oxygen uptake (V̇O_2max) and handgrip strength) and musculoskeletal pain among construction and health care workers. Additional aims were to analyse possible occupational differences in this association, and to relate self-reported physical activity to musculoskeletal pain and V̇O_2max.

This study aimed to examine the associations between individual capacity (V̇O_2max and handgrip strength) and musculoskeletal pain in construction and health care workers. Every second participant (51.8%) reported pain in either neck, shoulders or low back for more than 30 days during the last 12 months. The associations between individual capacity (V̇O_2max and handgrip strength) and musculoskeletal pain showed occupational differences; specifically, increased individual capacity was associated to lower musculoskeletal pain for health care workers but not for construction workers.

Previous studies on health care workers have examined the associations between physical capacity or physical activity and musculoskeletal pain. One study concluded that self-assessed low physical capacity was a strong predictor for developing non-chronic and persistent low back pain among health care workers [12]. Other studies showed associations between the level of physical activity and work ability [25] and between the level of physical activity and sickness absence among health care workers [26]. These studies did not include V̇O_2max or strength tests in their analyses, but the conclusions were in accordance with those from our study. In contrast, one study examined risk factors for low back pain among female nursing personnel and revealed that low self-assessed fitness and low physical activity were not among the risk factors [27]. Intervention studies may give some information on the effect of activity or changed individual capacity on risk for musculoskeletal disorders, but these studies have presented conflicting results. One intervention study that aimed at reducing musculoskeletal pain among health care workers showed positive effects of Zumba and football exercise on neck and shoulder pain, but not on low back pain [28]. Another study of lifestyle interventions among health care workers did not find effect on musculoskeletal pain [29]. These studies on health care workers had different design and measurements, which may explain the different results.

An exercise intervention designed to improve aerobic capacity among construction workers showed no effect on musculoskeletal pain [19]. Strength training for this occupational group showed no effect on shoulder pain [30]. An exploratory study in construction workers, which included self-reported physical fitness in the analyses, did not mention physical fitness among the factors related to musculoskeletal pain [31]. The results from our study confirmed the results from these studies. The lack of association between individual capacity and musculoskeletal pain among construction workers found in our study, may be due to larger effect on pain of other risk factors such as awkward work postures. This may also explain the lack of an effect of exercise interventions in this group.

The two sectors were gender-segregated, and it was not possible to distinguish between gender and profession. The results showing occupational differences may have exposed gender differences as well as occupational differences. The review from the Swedish Work Environment Authority on work-related MSDs and physical activity pointed out the lack of previous research focusing on gender differences, but it showed that the association between physical activity and musculoskeletal pain was more clear in studies that only included women [8]. The results from our study support this finding. Our results from the analysis with low back pain as the outcome variable can be compared with those of the aforementioned study in female health care workers, as that study revealed an association between low physical capacity and increased low back pain [12]. An association was found in our study between low back pain and individual capacity in mainly female health care workers, but not among male construction workers. A 6.5-year follow-up study in young adults examined the association between leisure time physical activity and low back pain. Even though that study did not reveal a clear relationship between physical activity and low back pain, a trend was found in females [32]. Contrary to this gender-related association, increased aerobic fitness among male conscripts aged 18–19 years was moderately associated with a reduced risk of non-injury musculoskeletal sickness absence 5–15 years later [33]. Previous gender-segregated studies were not conclusive.

To understand the different results in the two occupational groups, we explored the different characteristics between the groups. The health care workers had a significantly lower V̇O_2max and strength than that of the construction workers, which was predicted because women’s maximal aerobic capacity and muscular strength are lower than those of men [2, 34]. A conceptual model that included exposure, dose, capacity, and response illustrated a possible mechanism between low levels of muscular strength and musculoskeletal pain [7]. Exposure referred to external factors, in this context, work requiring considerable muscle force. The ability to “resist” doses of this exposure is determined by the muscle strength capacity. A high load repeated over time may lead to tissue damage, inflammation of the musculoskeletal tissue, and pain. These changes may result in reduced capacity and, in this context, reduced pain-dependent strength [7]. An adaption of the musculoskeletal tissue presupposes a mechanical exposure and recovery that are customized to the individual. Individuals with low muscular strength use a greater proportion of their maximum capacity than individuals with greater strength to perform the same work and will reach an assumed level of risk for tissue damage and pain faster [2]. The same model may illustrate the mechanism involved in the association between the level of VO_2max and musculoskeletal pain. The ability to manage work demanding a high energy metabolism may be determined by the aerobic capacity [2]. The model only fit our results for health care workers. With a lower V̇O2_max and strength, the gap between work demand and individual capacity seemed to be larger for health care workers than construction workers. A low capacity may lead to an increased risk of pain development, and a higher capacity may be a possible modifier. This relationship was not found for construction workers, in whom other work-related factors were more strongly associated with musculoskeletal pain.

Genetic contributions to individual capacity are important, but aerobic capacity and muscular strength are largely determined by the level of physical activity [35]. Physical activity is assumed to have an independent preventive effect on musculoskeletal pain. We also found a significant association between self-reported physical activity and musculoskeletal pain in health care workers but not in construction workers, although there were no significant differences in self-reported physical activity between the groups. Previous research had shown that self-reported physical activity and measured V̇O_2max were correlated but that the correlation was low [36] or moderate [37]. These results were supported by our data. The moderate correlation may be due to the limitations associated with self-reports [38], as participants may have had trouble remembering and averaging values of physical activity 1 year previously. Another possible explanation is that the levels of V̇O_2max and strength were the central factors associated with musculoskeletal pain rather than physical activity. A study in a working population supported this explanation and concluded that physical fitness showed a higher association with low back pain compared to self-reported physical activity. The authors suggested that for the prevention of pain, physical activity should be performed at an intensity and at a duration that contribute to an increased V̇O_2max [39].

Exercise programs at the workplace initiated to reduce musculoskeletal pain showed mixed results [8]. Exercise may not reduce symptoms for all workers with musculoskeletal pain, but the results from our study may help identify the groups to be focused upon. Our results indicate that activities promoting individual capacity may reduce musculoskeletal pain for health care workers.

This study revealed occupational differences in the association between V̇O_2max, handgrip strength, and musculoskeletal pain. Small but statistical significant associations were found for health care workers but not for construction workers. Due to the gender-segregated sectors included in this study, it was not clear whether the differences were related to occupation or gender. Increased levels of V̇O_2max and strength were associated with less musculoskeletal pain in health care workers, which indicate that activities promoting higher V̇O_2max and hand strength may reduce musculoskeletal pain in this group. However, this is a small study and results should be interpreted cautiously. Further research with a similar design but larger samples is needed to determine whether there are occupational and gender differences in the association between V̇O_2max, strength, and musculoskeletal pain.