Abstract
Age related neuromuscular changes include motor unit atrophy and neuromuscular junction destabilization. These changes decrease muscle force output and modulation, and increase motor output variability, leading to joint instability. One compensatory mechanism used to combat joint instability and enhance postural control in older adults is increasing muscle coactivation during tasks like gait. However, the time-continuous nature of multi-muscle coactivation patterns have not been explored to identify during what percentage of the gait cycle alterations emerge. PURPOSE: To identify the effects of aging on continuous multi-muscle coactivation patterns in the knee and ankle joints during gait using statistical parametric mapping (SPM). METHODS: Publicly available data was used, including 45 young (Age: 28.4 ± 5.1 yrs, Height: 172.7 ± 8.6 cm, Weight: 75.7 ± 18.4 kg) and 40 old (Age: 76 ± 6.3 yrs, Height: 164.3 ± 10.5 cm, Weight: 75.3 ± 11.4 kg) participants. Electromyographic data was obtained (1000 Hz) from the tibialis anterior (TA), gastrocnemius medialis (Gm), rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF), and semitendinosus (ST) of the right leg during right stride. Electromyographic traces were band-pass filtered with a 2nd-order Butterworth filter (10-300 Hz) and linear enveloped. The time-varying multi-muscle coactivation (TMCfi) was computed based on the following equation: $\mathrm{TMC}_f\!\left(d(t),t\right)=\left(1-\frac{1}{1+e^{-12\left(d(t)-0.5\right)}}\right)\ast\frac{\left(\sum_{i=1}^{N}\dfrac{\mathrm{EMG}_i(t)}{100\,N}\right)^2}{\max_{i=1,\ldots,N}\left[\mathrm{EMG}_i(t)\right]}$, where EMGi denotes the amplitude of the ith EMG at time sample, t, and d(t) denotes the mean difference between each EMGi(t) pairing. The TMCfi of the right knee joint was calculated using EMG data recorded from the RF, VL, BF, and ST, whereas that of the right ankle joint was calculated using EMG data from the TA and Gm. Finally, statistical parametric mapping (SPM) t-tests were used to analyze differences in TMCfi between healthy young and old adults. The significance level was set at ɑ = 0.05. All procedures were performed in MATLAB R2023b. RESULTS: The right stride right knee TMCfi revealed no statistical significance between healthy young and old adults. However, older adults displayed significantly greater right ankle coactivation during 30.3%-31% (|t*|= 3.3966, P = 0.044) and 31.65%-33.65% of the right stride (|t*|= 3.4612, P = 0.045). CONCLUSION: Older adults exhibit greater right ankle muscle coactivation at ~30% to 34% of the gait cycle, corresponding to the midstance phase. During this phase, body weight is supported by the reference foot and the center of gravity is at its highest vertical position, requiring greater joint stabilization. Due to age-related neuromuscular alterations and fear of falling, older adults employ greater ankle coactivation presumably to increase lower extremity active stiffness and reduce joint movement variability. Moreover, this increase may improve the transition from shock absorption to forward propulsion. While this increase in coactivation may lead to greater joint stability, it could also be interpreted as a reduction in joint adaptability, a potential counter justification which requires further investigation.
Recommended Citation
Champion, Reece K.; Hoang, Kiefer A.; and Alighanbari, Mohsen
(2026)
"Effects of Aging on Time-continuous Lower Extremity Multi-muscle Coactivation Patterns During Gait,"
International Journal of Exercise Science: Conference Proceedings: Vol. 2:
Iss.
18, Article 82.
Available at:
https://digitalcommons.wku.edu/ijesab/vol2/iss18/82