Author(s): ROUSSEL, M., PAPAXANTHIS, C., TIMBERT, T., PAIZIS, C., Institution: UNIVERSITY OF BURGUNDY, Country: FRANCE, Abstract-ID: 2735

INTRODUCTION:
Age-related decline in muscle strength is a major determinant of functional dependence in very old adults. The quadriceps plays a key role in mobility, balance, and fall prevention, making it a primary therapeutic target. Although resistance exercise is effective in attenuating strength loss, frail older individuals may have limited tolerance to increased mechanical loading or training volume.
Local vibration (LV), applied directly to a tendon, increases Ia afferent input and may enhance motor unit recruitment when superimposed on voluntary contractions. This strategy could theoretically increase internal neuromuscular load without raising external mechanical demand, thereby representing a potentially suitable approach for frail populations. However, its acute effects during repeated maximal isometric contractions in very old adults remain unclear.
This study examined whether superimposed LV modifies mean force production and fatigue development during repeated maximal voluntary isometric contractions (MVIC) of the quadriceps.

METHODS:
Twenty-four institutionalized older adults (85.8 ± 7.5 years) participated in this randomized crossover study. Participants completed two experimental conditions separated by 24 h and performed at the same time of day (≤ 60 min). In each condition, four MVIC of the right quadriceps were performed in a standardized seated position (knee flexed at 90°). Each contraction lasted 30 s and was separated by 60 s of passive recovery. Mean force over the 30-s contraction was continuously recorded using a push dynamometer. In the LV condition, mechanical vibration (100 Hz, 2 mm amplitude) was applied to the quadriceps tendon throughout each contraction; no vibration was applied in the control condition. Condition order was randomized.
RESULTS:
Mean force significantly declined across repetitions (F(3,69) = 3.62, p = 0.017, ηp² = 0.14), indicating neuromuscular fatigue. A significant main effect of condition was observed (F(1,23) = 5.51, p = 0.028, ηp² = 0.19), with overall lower force production in the LV condition. No condition × repetition interaction was found (F(3,69) = 0.44, p = 0.725, ηp² = 0.02), indicating that LV did not alter the fatigue pattern. The fatigue index (repetition 1 to 4) was −6.8% in control and −11.3% in LV.
CONCLUSION:
Superimposed LV during maximal isometric contractions did not enhance neuromuscular output and resulted in lower overall mean force, without modifying fatigue progression. Under the present parameters, LV does not appear to increase acute internal neuromuscular load in very old adults and may interfere with effective force generation. Alternative vibration settings or submaximal paradigms should be investigated to determine potential benefits in this frail population.