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The influence of aging on the isometric torque sharing patterns among the plantar flexor muscles

Oliveira L. F., Verneque D., Menegaldo L. L.

Acta of Bioengineering and Biomechanics

2017

Vol. 19, no. 1

41--45

Purpose: Physiological cross-sectional area (PCSA) reduction of the triceps surae (TS) muscles during aging suggests a proportional loss of torque among its components: soleus, medial and lateral gastrocnemii. However, direct measurements of muscle forces in vivo are not feasible. The purpose of this paper was to compare, between older and young women, isometric ankle joint torque sharing patterns among TS muscles and tibialis anterior (TA). Methods: An EMG-driven model was used for estimating individual muscle torque contributions to the total plantar flexor torque, during sustained contractions of 10% and 40% of maximum voluntary contraction (MVC). Results: Relative individual muscle contributions to the total plantar flexion torque were similar between older and young women groups, for both intensities, increasing from LG, MG to SOL. Muscle strength (muscle torque/body mass) was significantly greater for all TS components in 40% MVC contractions. Increased TA activation was observed in 10% of MVC for older people. Conclusions: Despite the reduced maximum isometric torque and muscle strength, the results suggest small variations of ankle muscle synergies during the aging process.

Input error analysis of an EMG-driven muscle model of the plantar flexors

de Oliviera L.F., Menegaldo L.L.

Acta of Bioengineering and Biomechanics

2012

Vol. 14, no. 2

75-81

EMG is a useful tool for quantifying muscle forces and studying motor control strategies. However, the relationship between EMG and muscle force is not trivial, and depends in part on muscle dynamics. This work has the following objectives: the first, to find muscle excitations and partial joint torque contribution patterns in isometric plantar flexions, considering low and medium/high contractions. The second, to correlate such patterns with an EMG-driven muscle model error, indirectly assessed by the associate joint torques. Individual muscle contributions were calculated using the model driven by the measured EMG and compared to the total joint torque from dynamometric measurements. Thirteen young males performed a protocol with low and medium/high intensities contractions. Input functions were the normalized EMG of each triceps surae and tibialis anterior muscles. RMS error was calculated between the measured and estimated torque curves. The trends observed were: the order of individual muscle contributions to the total torque (SOL, GM, GL) was different from the order of the contraction intensities (GM, SOL, GL); the model was more accurate for medium/high contractions; the worst estimations occurred when excitation input signals found from EMG were underestimated. Possible causes for such errors and improvement suggestions are addressed.