The aims of this study were to describe the patterns of self-reported physical activity and sedentary behaviour in people with MG and to explore associations between these health-related behaviours and fatigue, quality of life, walking limitation and balance confidence. The findings of this study indicate that despite over two-thirds of the participants meeting physical activity guidelines, over a quarter also spend over 10 hours sitting per day. Further, participants largely met guidelines through accruing moderate-intensity physical activity, with less than half of all participants engaging in any vigorous activity at all. There were significant associations found between meeting physical activity guidelines and less fatigue, greater quality of life, less walking limitation and greater balance confidence, while conversely no associations were found between these variables and sedentary behaviour alone. However there were also significant dose-response relationships between patterns of physical activity and sedentary behaviour, with those that were inactive but accruing < 10 h/day of sedentary time significantly associated with less fatigue, greater quality of life, less walking limitation and greater balance confidence compared to those that are inactive but reported sitting ≥ 10 h/day.
The Australian Physical Activity Guidelines recommend 150 minutes per week of moderate-vigorous physical activity in order to attain significant health benefits (46), which equates to 500 METminutes.wk− 1. Two-thirds of the participants in our study were classified as sufficiently active, however less than half of this sufficiently active group engaged in any vigorous physical activity. This is slightly lower than a previous study investigating physical activity and sedentary behaviour in 27 adults with MG (mean age 62 ± 16 years), which reported that 78% of participants reached physical activity guidelines, however only 11% engaged in ≥ 20 min/day of vigorous activity for a minimum of three days per week (25). It is important to note that this previous study used device-based measures of physical activity, whereas the current student utilised self-report which typically results in higher estimates of physical activity (47). There is a possible recruitment bias as the cross-sectional study was a part of a larger study that included a training opportunity for participants. Subsequently, those recruited may have had an interest in physical activity that influenced the cross-sectional data. Given the additional health benefits of vigorous physical activity (48), further investigation into the barriers to vigorous activity in this population is warranted.
Regarding sedentary behaviour, similar findings were reported in both our own and the aforementioned study, with high levels of sedentary behaviour in both (25). Our findings indicate the median daily sedentary time among participants was approximately 9 h/day (8.98 ± 3.53), 2.5 hours more than found in the general adult population in one study (n = 3,699), where average self-report sedentary behaviour was 6.5 h/day (95% CI 6.2–6.7)(49). This is also higher than findings in other neurological populations; one study in adults with multiple sclerosis reported average self-report sedentary time of 7.5 ± 3.7 h/day (n = 1081) (50). The medical advice and benefits of exercises in multiple sclerosis has evolved greatly over the past two decades and the overall lower sedentary time for this group may be reflective of this. Given the evidence for higher sedentary time and poor health outcomes including increased mortality (51), further interventional research to reduce sedentary time in people with MG is needed to reduce these risks.
In the present study, significant associations were found between physical activity and fatigue, quality of life, walking limitation and balance confidence. This is the first study, to our knowledge, that has explored this in people with MG. In other populations physical activity interventions have shown positive effects on fatigue (52–54), quality of life (55), walking ability (55, 56) and balance (56). Pathologies associated with impaired movement such as in MG may result in reduced capacity for physical activity and more sedentary behaviour, thereby risking physiological effects from disuse. The positive benefits in the above studies may be a direct consequence of breaking this disuse cycle, restoring the physiological deficits from disuse and/or having an impact on the primary symptoms of the pathologies (20). At this stage for people with MG it is unclear whether the participants who engage in more physical activity, do because they are less fatigued, have better quality of life, less walking limitation and/or greater balance confidence and thus able to break this disuse cycle, or the other way around. Longitudinal research is warranted to investigate these relationships further and determine direction of associations and treatment impacts. Nonetheless, these preliminary findings are of important clinical consideration given the historical concerns of increased activity leading to provocation of symptoms in this population. Overall, our findings support the growing body or literature that higher levels of exercise and physical activity do not appear to be associated with negative outcomes in people with MG and may in fact have similar positive outcomes as seen in healthy populations. However, despite the statistical significance, R2 values in our study are low and so our findings should be interpreted with caution.
Although there were no associations found between sedentary behaviour alone and the outcomes assessed in this study, there were significant associations with these variables when patterns of sedentary behaviour were analysed in combination with sufficient versus insufficient physical activity. Our findings indicate that even in those who are inactive, lower levels of sedentary time (< 10 h/day) are associated with less fatigue, higher quality of life, less walking limitation and greater balance confidence compared to those with higher sedentary time (≥ 10 h/day). This is a promising finding, potentially suggesting that sedentary behaviour may be an appropriate intervention target even when physical activity levels are low. The potential protective effect of physical activity against the detriments of sedentary behaviour is another consideration in this population. A recent meta-analysis found that the increased mortality risk associated with high sedentary time appears to be mitigated with increasing physical activity levels and even reversed in those who are in the highest quartile for physical activity (> 2130 METminutes.wk− 1) (15). These findings indicate that changing sedentary time has a positive effect on mortality irrespective of physical activity levels, and so warrants further investigation as to a potential target intervention for people with MG, given that the findings of our study indicate high levels of sedentary behaviour in this population. As these benefits are most impactful when combined with higher levels of physical activity, interventions targeting whole of day activity and thus incorporating both physical activity and sedentary behaviour may be of benefit in improving health and well-being outcomes in adults with MG.
The findings of this study should be considered in light of a number of limitations. The cross-sectional design gives insight into these behaviours at only one point in time and therefore limits the ability to determine causality. Further longitudinal and/or interventional research is needed to determine direction of associations and efficacy, respectively. Most of our participants reported generalised (n = 92, 96.5%) compared with ocular-only symptoms (n = 3, 3.5%); an underrepresentation of people with symptoms limited to the ocular muscles. Ocular-only MG is estimated to occur in approximately 17% of MG cases and around half will then progress to generalised symptoms (57). Despite symptoms only affecting the ocular muscles, associated symptoms such as diplopia are common in this type of MG (3) and can impact on function in daily tasks (58), and as such we opted to include both ocular and generalised in the analysis.
Self-report measures were utilised for both physical activity and sedentary behaviour, which can lead to over-reporting by participants (47) and be inaccurate when compared with objective device-based monitoring (59). Additionally, these measures were not specific to MG as no such MG specific measures of physical activity or sedentary behaviour are currently available. Despite limitations in the use of self-report measures, a strength of this type of measure is the ease of distribution which facilitated a larger sample size for our study (n = 85) than what has been used in prior related research (n = 27) (25). Given the low incidence of MG and subsequent recruitment difficulties, using an electronic self-report survey enabled recruitment across a larger geographical area. This method, however, limited our capacity to classify disease severity amongst participants given the lack of face to face clinical assessment and absence of a single universally acceptable classification of severity in this population (60). Prior research, although limited, suggests there is no relationship between disease severity and physical activity in this population (25), however further high-quality evidence is required to investigate this further. Finally, the R2 values of our models was generally low, indicating that there may be a number of other variables contributing to these relationships.