Kinematics and muscle activation patterns during a maximal voluntary rate activity in healthy elderly and young adults.

BACKGROUND: Maximal voluntary rate (MVR) performance tasks can provide important age-related information to the limiting factors associated with movement and the development of fatigue.

AIM: To determine whether kinematic and muscle activation patterns during an MVR task differ between young and older adults.

METHODS: We continuously measured frequency, amplitude, peak velocity, index of co-contraction and median frequencies of the index finger flexors and extensors during a 20-s MVR task in 10 young and 10 older subjects.

RESULTS: Index finger amplitude and peak velocity in flexion and extension were significantly lower in the older group. During the MVR, amplitude was maintained in the old (1-4 s, 53.2° ± 2.8° vs. 15-19 s, 48.6° ± 3.2°, ns) but not in the younger group (1-4 s, 64.9° ± 4.9° vs. 15-19 s, 59.4° ± 3.3°; p = 0.001). Frequency declined in the young (1-4 s, 5.2 ± 0.24 Hz vs. 15-19 s, 4.4 ± 0.25 Hz; p = 0.001) and old (1-4 s, 4.6 ± 0.17 Hz vs. 15-19 s, 4.0 ± 0.15 Hz; p = 0.01). Similarly, peak flexion velocity of the young (1-4 s, 1.77 ± 0.07 × 103  °/s vs. 15-19 s, 1.01 ± 0.07 × 103  °/s, p = 0.01) and older groups (1-4 s, 1.04 ± 0.07 × 103  °/s vs. 15-19 s, 0.78 ± 0.06 × 103  °/s; p = 0.016) as well as peak extension velocity of the young (1-4 s, 1.01 ± 0.053 × 103  °/s vs. 15-19 s, 0.78 ± 0.06 × 103  °/s, p = 0.01) and older groups (1-4 s, 0.72 ± 0.04 × 103  °/s vs. 15-19 s, 0.58 ± 0.05 × 103  °/s, p = 0.012) significantly decreased throughout the MVR. Median frequency of the flexors and extensors were maintained and were not different between groups. Only the older group experienced an increase in the index of co-contraction.

CONCLUSION: The changes in kinematics over time are not a result of a decrease in pre-post test force or velocity, but rather central factors affecting movement coordination.