Acute and Repeated Bout Effects of Sub-Maximal Isokinetic Eccentric Exercise on Neuromuscular Function and Perceived Exertion in Older Adults.

Introduction
The superior muscular adaptations accompanied by lower metabolic demand commonly reported following eccentric exercise make it highly suitable to combat age-related neuromuscular decline [1]. However, acute decreases in strength are often observed alongside muscle soreness following eccentric contractions [2], although these symptoms are usually alleviated following the initial exposure (i.e. “the repeated bout effect” [RBE]). Whilst muscle strength and soreness are commonly examined, few studies investigate other common fall-risk factors. Therefore, the present study examined the acute and RBE of eccentric exercise on neuromuscular fall-risk factors and perceived exertion in older adults.
Methods
Neuromuscular function (sit-to-stand, timed-up-and-go [TUG], isometric and eccentric strength, explosive capacity, and postural sway) and rate of perceived exertion (RPE) whilst performing functional tasks were measured in 13 participants (age = 67.6 ± 4.9 y) pre- and post-eccentric exercise (0, 24, 48 and 72 h) in bout 1 (acute) and 14 days later in bout 2 (RBE). Eccentric exercise was performed on an isokinetic unilateral stepper ergometer at 50% of maximal eccentric strength for seven minutes (including 1 min warm-up and cooldown) at 18 step/min (126 steps per limb). Two-way repeated measures ANOVAs and post-hoc analyses were conducted to identify any significant (P < 0.05) differences.
Results
Eccentric strength significantly decreased in bout 1 at 24 h post-exercise then recovered; no significant reduction occurred in bout 2. Rate of torque development (0-200 ms) significantly decreased in both bouts at 24 h post-exercise but then recovered; contractile impulse (0-250 ms) did not decrease in bout one but did at 24 h post-exercise in bout 2 and then recovered. No significant reduction occurred in any other neuromuscular function measure in either bout. RPE during sit-to-stand remained significantly elevated for 72 h post-exercise in bout 1 but was only elevated immediately post-exercise (0 h) during bout 2. RPE during TUG remained significantly elevated for 72 h after both bouts of exercise.
Conclusion
Sub-maximal eccentric exercise results in minimal disruption to neuromuscular functional characteristics that are commonly associated with falls in older adults after the initial bout, which were eliminated in bout 2, indicative of a protective RBE. Low levels of muscle soreness evident after the initial exposure were also alleviated following the second bout. Despite no change in sit-to-stand or TUG performance, RPE was elevated when conducting these tasks. Nonetheless, the present findings suggest that sub-maximal low-volume eccentric exercise is a safe exercise modality to prescribe to community-dwelling older adults given the minimal impact on fall-risk characteristics.
References
1. LaStayo et al. (2014). J Appl Physiol. 116:1426-1434.
2. Hody et al. (2019). Front Physiol. 10:536.