Background: Muscle force output during sustained submaximal isometric contractions fluctuates around an average value, partly due to variations in motor unit firing rates (1). Although 4-weeks targeted force accuracy training (FAT) has been shown to improve muscle force control in younger adults (2), little is known about the impact of these interventions in healthy older adults, or the impact on the untrained limb following unilateral training. Therefore, we investigated whether short-term unilateral FAT could improve muscle function in the trained and untrained limbs of older adults.
Methods: This study was approved by the University of Nottingham Faculty of Medicine and Health Sciences Research Ethics Committee (FMHS 390-1121). After providing written, informed consent to participate, 16 healthy participants (8 male, 8 female. 74±5 years, BMI 26±3 kg/m2) underwent two assessment visits separated by 4-weeks fully-supervised unilateral knee extensor FAT. FAT occurred 3x/wk and consisted of 6 sinusoidal force-tracking contractions at 10, 25 and 40% of maximum voluntary contraction (MVC) in each session. Bilateral knee extensor strength was assessed via MVC and the coefficient of variation of force (force steadiness (FS)) was quantified at 25% MVC. Left and right handgrip strength (HGS) were measured with a handheld dynamometer, and mobility was assessed by the timed up-and-go (TUG). Data were analysed via two-way repeated measures ANOVA (leg/hand x time) and paired Students t-test (TUG). Statistical significance was accepted at p<0.05.
Results: There was no leg x time interaction for MVC (p=0.822), but there was a main effect of time (p=0.003) with MVC increasing in the trained (+15.2%, p=0.04) but not the untrained (p=0.09) limb. There was a significant leg x time interaction (p=0.026) for FS, improving to a greater extent in the trained (+16.2%, p=0.0001) than the untrained (+8.9%, p=0.041) limb. There was no hand x time interaction for HGS (p=0.885), however there was main effect of time (p=0.001) with HGS improving in the right (+3.2% p=0.04) and left (+3.8%, p=0.028) hand. There was a significant improvement in TUG time following the FAT intervention (p=0.023).
Conclusion: In older adults, 4-weeks unilateral FAT leads to improved bilateral muscle force control, improved strength of the trained limb and increased bilateral HGS. Importantly, the FAT also improved TUG performance, an important measure of functional ability in older age. These findings demonstrate that low-intensity FAT is able to elicit targeted and cross-education improvements in muscle function. This may inform the development of interventional strategies to improve muscle function in older clinical populations (i.e., as prehabilitation for surgery given its impact in a short time-frame (3)), including in age-associated conditions with unilateral symptom presentation (i.e., stroke) (4).