Background Older adults often experience impaired mobility, lower extremity muscle weakness, and increased fall risk. Furthermore, when older adults perform tasks that require control of submaximal force, impairments in their ability to maintain steady and accurate force output has been reported. Such problems may be related to deteriorating levels of mobility, particularly in older adults who have fallen. Purpose The purpose of this study was to determine whether an association exists between muscle force steadiness (MFS) or muscle force accuracy (MFA) of the knee extensors and mobility in older adults who have fallen. Methods Twenty older adults (x̄ = 77.5 ± 7yrs, 5 males and 15 females) with 2 or more co-morbid conditions and who experienced a fall in the past year underwent assessment of maximal voluntary isometric contraction (MVIC) of the knee extensors. A submaximal target force of 50% of their MVIC was used to determine concentric (CON) and eccentric (ECC) steadiness (the fluctuations in force production) and accuracy (the average distance of the mean force from the target force) measures. Mobility was indicated by the 6 minute walk test (6MWT), the timed up and go (TUG), stair ascent (StA), and stair descent (StD) tests. Correlation analysis was used to assess the relation between measures of muscle force control and mobility. Results The correlations between MFS and mobility were not significant (p>0.05) for either contraction type. However, MFA during ECC contractions only, were correlated significantly with all measures of mobility: 6MWT (r=−0.48, p=0.03), TUG (r=0.68, p=0.01), StA (r=0.60, p=0.01), StD (r=0.75, p<0.01). Conclusion The identification of the relationship between ECC MFA and mobility in older adults who have fallen is novel. While the correlations are not causal, these relationships suggest inaccurate force output during ECC contractions of the knee extensors is linked to impaired mobility.

The motor skill required to decrease the variability in muscle force steadiness can be challenging. The purposes of this study were to determine whether muscle force steadiness improved following repeated trials and whether the number of trials varied for healthy younger adults, healthy older adults, and older adults who have fallen to obtain stable muscle force steadiness measures. Sixty participants performed 30 concentric and eccentric contractions of the knee extensors on an isokinetic dynamometer. Each group had significant improvements in muscle force steadiness and obtained stable measures within six to nine trials. Healthy younger and older adults, and older adults who have fallen, can improve muscle force steadiness. These findings provide a framework for methodological approaches when testing steadiness in varying populations.