Dynamics and stability of muscle activations during walking in healthy young and older adults

Abstract

To facilitate stable walking, humans must generate appropriate motor patterns and effective corrective responses to perturbations. Yet most EMG analyses do not address the continuous nature of muscle activation dynamics over multiple strides. We compared muscle activation dynamics in young and older adults by defining a multivariate state space for muscle activity. Eighteen healthy older and 17 younger adults walked on a treadmill for 2 trials of 5 minutes each at each of 5 controlled speeds (80 -120% of preferred). EMG linear envelopes of v. lateralis, b. femoris, gastrocnemius, and t. anterior of the left leg were obtained. Interstride variability, local dynamic stability (divergence exponents) and orbital stability (maximum Floquet multipliers; FM) were calculated. Both age groups exhibited similar preferred walking speeds (p = 0.86). Amplitudes and variability of individual EMG linear envelopes increased with speed (p< 0.01), in all muscles but gastrocnemius. Older adults also exhibited greater variability in b. femoris and t. anterior (p < 0.004). When comparing continuous multivariate EMG dynamics, older adults demonstrated greater local and orbital instability of their EMG patterns (p < 0.01). We also compared how muscle activation dynamics were manifested in kinematics. Local divergence exponents were strongly correlated between kinematics and EMG, independent of age and walking speed, while variability and max FM were not. These changes in EMG dynamics may be related to increased neuromotor noise associated with aging and may indicate subtle deterioration of gait function that could lead to future functional declines.

Assessing the stability of human locomotion: a review of current measures

“…Another problem is how to perturb the state variables piece by piece. The first problem is usually solved by taking the mean of the trajectory crossings at a Poincaré section of a steady-state walking trial as an approximation of the fixed point [27,30,34,42,43,56,62,68,69,72,74,75,83,92,99,100], which is a reasonable assumption given that steady-state human walking has some degree of stability (i.e. humans can walk without falling every other step).…”

The role of physical activity in changes in walking mechanics with age

“…The underlying factors contributing to changes in walking performance in the aging population is unclear, but may include changes in muscle strength, balance, joint mobility and cardiovascular fitness [2,6,[11][12][13][14][15][16]. In-depth gait studies in the elderly suggest some factors underlying these gross changes in walking performance include decreases in joint ranges of motion [17], an increased reliance on hip musculature for power generation, and a reduction in the ankle joint moments and powers [4,7,[18][19][20] compared to healthy young control subjects.…”

Evaluation of upper limb muscle fatigue based on surface electromyography

“…Numerous studies [1, 13,14] have suggested that sEMG can reflect local muscle fatigue, as supported by the data in Ta- 90 …”

“…Many studies [7,12,13] have investigated muscle fatigue using mean power frequency (MPF), median frequency (MF) and root mean square (RMS) of sEMG. MF and RMS decrease continuously during muscle fatigue, and MPF, MF and RMS can be used to characterize the physiological indicators of muscle charge.…”