Immediate voluntary activation deficits following submaximal eccentric contractions of knee extensors are associated with alterations of the sense of movement

Abstract

The mechanisms underlying movement sense alterations following repeated eccentric contractions remain unclear. This study concomitantly investigated the effects of unilateral eccentric contractions on movement sense and on neuromuscular function at the knee before, immediately after (POST), 24 (POST24) and 48 (POST48) h after the exercise. Twelve participants performed sets of submaximal knee extensors (KE) eccentric contractions until a 20% decrease in maximal voluntary isometric contraction (MVIC) torque was reached. Threshold to detect passive movement (TTDPM) tasks were used to assess movement sense during both knee flexion (TTDPM_FLEX) and extension (TTDPM_EXT). KE fatigability was assessed using the interpolated twitch technique. TTDPM values expressed in seconds and the percentage of unsuccessful trials only increased at POST during TTDPM_FLEX and TTDPM_EXT. The 20%-MVIC decrease was associated with significant decreases in voluntary activation level (- 12.7%, p < 0.01) and potentiated doublet torque at 100 Hz (- 18.1%, p < 0.001). At POST24, despite persistent reductions of maximal voluntary and electrically evoked torques associated with increased perceived muscle soreness, TTDPM values and the percentage of unsuccessful trials returned to baseline values. Consequently, movement sense alterations were only observed in the presence of voluntary activation deficits, suggesting that some exercise-induced central alterations may affect the somatosensory function.

Figure 1

Overview of the experimental protocol. Neuromuscular and psychophysical evaluations were performed before (PRE) and immediately after (POST) a unilateral fatiguing eccentric exercise at the knee. PRE evaluations were similarly performed 24 (POST24) and 48 (POST48) hours after the eccentric exercise, without the familiarization period. Please refer to the text for further explanations. KE Knee extensors, ECC Maximal voluntary eccentric contraction, MVIC Maximal voluntary isometric contraction.

Figure 2

Effects of the submaximal eccentric exercise on knee extensor’s neuromuscular function. Percent changes from pre-exercise values in (a) maximal voluntary torque production (MVIC in black bars and ECC in white bars), (b) VA , (c) Dt_{100 Hz} and (d) Dt_{10 Hz}. *, ** and ***Significantly different from PRE values at p < 0.05, p < 0.01 and p < 0.001, respectively. MVIC Maximal Voluntary Isometric Contraction, ECC Maximal voluntary eccentric contraction, VA Voluntary Activation level, Dt_{100 Hz} potentiated doublet amplitude at 100 Hz, Dt_{10 Hz} potentiated doublet amplitude at 10 Hz. The statistical analyses of this figure were performed using Statistica software.

Figure 3

Effects of the eccentric exercise on knee movement sense. (a) TTDPM best trial values and (b) percentages of unsuccessful trials during TTDPM tasks before (PRE), immediately after (POST), and 24 (POST24) and 48 (POST48) hours after the eccentric exercise. ^* and ^**Significantly different from PRE values at p < 0.05 and p < 0.01, respectively. TTDPM_FLEX Threshold To Detect Passive Movement into flexion at 30° of knee flexion, TTDPM_EXT Threshold To Detect Passive Movement into extension at 30° of knee flexion. The statistical analyses of this figure were performed using IBM SPSS software.