Background: Understanding the root cause of the age-related impairment in muscle adaptive remodelling with resistance exercise training (RET) and developing pragmatic and accessible resistance exercise for older adults, are essential research directives. Methods: We sought to determine whether indices of quadriceps muscle EMG activity in response to different modes of RET and activities of daily living (ADL), differed between 15 healthy younger (25 ± ۳ years) and 15 older (70 ± ۵ years) adults. On four separate days, participants completed a maximal voluntary contraction (MVC) of the knee extensors, followed by a 15 m walking task, stair climbing task (i.e. ADL) and lower-limb RET through body-weight squats (BW-RET) and seated knee extensions on a machine (MN-RET) or via elastic bands (EB-RET). Surface quadriceps electromyography (EMG) was measured throughout all tasks to provide indirect estimates of changes in muscle activity. Results: MVC was significantly greater in young vs. older adults (Young: 256 ± ۷۲ vs. Old: 137 ± ۴۸ N·m, P < 0.001). EMG activity during all exercise tasks was significantly higher in older vs. younger adults when expressed relative to maximal EMG achieved during MVC (P < 0.01, for all). In addition, relative quadriceps muscle EMG activity was significantly greater in EB-RET (Young: 20.3 ± ۸٫۷ vs. Old: 37.0 ± ۱۰٫۷%) and MNRET (Young: 22.9 ± ۱۰٫۳, vs. Old: 37.8 ± ۱۰٫۸%) compared with BW-RET (Young: 8.6 ± ۲٫۹ vs. Old: 27.0 ± ۹٫۳%), in young and older adults (P < 0.001). However, there was no significant difference in quadriceps EMG between EB-RET and MN-RET (P > 0.05). Conclusions: In conclusion, relative quadriceps muscle EMG activity was higher across a range of activities/ exercise modes in older vs. younger adults. The similar quadriceps muscle EMG activity between EB-RET and MN-RET provides a platform for detailed investigation of the neuromuscular and muscle metabolic responses to such pragmatic forms of RET to strengthen the evidence-base for this mode of RET as a potential countermeasure to sarcopenia.
Ageing is associated with a precipitous loss of skeletal muscle strength, quantity/quality and functional capacity (termed sarcopenia) (Cruz-Jentoft et al., 2020; Rosenberg, 1997). Sarcopenia progresses at a rate of ~0.7–۱٫۲%/year after the 5th decade of life (Mitchell et al., 2012), and is associated with a loss of independence (dos Santos et al., 2017) and increased morbidity and mortality risk (Brown et al., 2016). The prevalence of sarcopenia within the UK, in community-dwelling older adults (> 65 years), has been reported to be > 12.5% (Patel et al., 2013), rising to > 20% in those aged > 85 years (Dodds et al., 2017). Alarmingly, > 78% of older adults admitted to primary care and inpatient facilities are diagnosed with this condition (Rubio-Maicas et al., 2014). Ultimately, sarcopenia presents a considerable burden on healthcare resources (Goates et al., 2019) that will continue to rise as prevalence increases (Ethgen et al., 2017). Evidence from randomised control trials (Leenders et al., 2012; Snijders et al., 2019; Verdijk et al., 2009), systematic reviews and meta-analyses (Peterson et al., 2010; Peterson et al., 2011) demonstrates that regular, progressive resistance exercise training (RET) can effectively attenuate/counteract sarcopenia and alleviate many of its adverse health consequences. However, the muscle adaptive remodelling response to RET may be compromised in older age (Greig et al., 2011). Specifically, there is strong evidence that the muscle protein synthetic (MPS) response to RET is blunted in older, compared with younger, adults (Brook et al., 2016). This is important as RET-induced MPS stimulation is a key determinant of the overall net protein balance/accretion for muscle hypertrophy (Morton et al., 2018). However, the underlying cause of this muscle anabolic resistance in older age is unclear and, therefore, warrants further investigation in order to maximize the health benefits of RET in older adults.