Local exercise based on voluntary contractions produces greater warm-up effects on balance control than electro-induced contractions.

On the one hand, while general (involving the whole body) warm-up exercises have been extensively used to optimize motor and postural performance, the effect of a local (involving a particular muscular group) warm-up has not yet been addressed. On the other hand, voluntary (VOL) and electro-induced (EI) contractions produce different physiological effects likely to differently affect motor and postural performance. The aim was to analyze and compare the effects of two local warm-up modalities, voluntary and electro-induced (VOL or EI warm-up) on balance control. Balance control was evaluated with a force platform (recording the displacement of the centre of foot pressure - COP) in 27 healthy young subjects before (PRE), immediately after (POST), 5 min after (POST5), and 10 min after (POST10) either warm-up. Each warm-up included 6 sets of 5 contractions at 10% of maximal voluntary contraction of the quadriceps femoris. The results showed that the VOL warm-up improved balance control at POST, POST5 and POST10 while the EI warm-up improved it only at POST10. In addition, balance control was significantly better after the VOL warm-up than after the EI warm-up at POST5 and POST10. A short and local VOL warm-up improved balance control immediately after its completion and for, at least, ten minutes, while the EI warm-up required some minutes of recovery before producing its improving effects.

The optimal exploitation of sensory electrical stimulation for regulating postural balance depends on participants' intrinsic balance abilities.

BACKGROUND: The sensory electrical stimulation applied to the postural muscles provides additional sensory information that improves postural balance but this improvement seems to be highly subject-dependent. RESEARCH QUESTION: The first aim was to analyse the effects of sensory electrical stimulation on postural balance and the second aim was to analyse these effects depending on intrinsic postural balance abilities of subjects. METHODS: Twenty healthy young male participants completed a monopedal postural task with sensory electrical stimulation (1 ms; 10 Hz; 7 ± 2 mA i.e., twice the intensity corresponding to the sensory threshold) and without sensory electrical stimulation. Pearson's product-moment correlations were performed on centre of pressure parameters to assess whether the participant's balance abilities at baseline were related to the beneficial effects of sensory electrical stimulation. RESULTS: The results showed positive correlations for all the variables measured (i.e., with r2 from 0.32 to 0.35). Evidence suggests that subjects' abilities to take advantage from electrically induced additional afferents depended on participants' intrinsic balance abilities. In fact, subjects who exhibited the worst postural balance at baseline (i.e. without stimulation) benefited more from the effects of sensory electrical stimulation than subjects who displayed the best postural balance at baseline. SIGNIFICANCE: In physically impaired subjects, as part of functional rehabilitation, sensory electrical stimulation would be particularly interesting in order to limit their risk of falling.

Effect of the application of somatosensory and excitomotor electrical stimulation during quiet upright standing balance.

Somatosensory (which activates sensory neurons only) and excitomotor (which activates both motoneurons and sensory neurons) electrical stimulations applied on the musculature of the lower-limb are likely to facilitate and disturb balance control respectively. The aim of this study was to compare the possible balance control modifications induced by somatosensory (SS) and excitomotor (EX) electrical stimulations applied on the quadriceps femoris in quiet standing condition. Kinetics and kinematics parameters were recorded with a force platform (displacements of center of foot pressure) and a 3D analysis system (hip, knee and ankle angles) respectively during a postural task. Twenty healthy young male participants carried out a monopedal postural task (i.e., unilateral stance) in three conditions: SS stimulation (1ms; 10Hz; 7±2 mA i.e., twice the intensity corresponding to the sensory threshold), EX stimulation (400 µs; 50 Hz; 20 ± 5 mA i.e., twice the intensity corresponding to the motor threshold), and a control (CONT) condition without stimulation. The results showed no significant differences between the three conditions except for the knee' angle which was higher in the EX condition (167.3±11.6 vs 164.3±5.8 and 163.9±8) (p < 0.005) than in the two other conditions (SS stimulation and CONT). This means that the EX stimulation induced a postural position change (i.e., a slight knee extension) during the monopedal postural task without altering balance control. Overall, on the basis of the stimulation parameters used in the present work, neither the SS stimulation, nor the EX stimulation facilitated or disturbed postural balance.

Correction to: Voluntary and electrically-induced muscle fatigue differently affect postural control mechanisms in unipedal stance.

In the metadata of the original publication of the article.