- Written by Nicola A. Maffiuletti, Switzerland and Grégory Dupont, France
INTRODUCTION AND RATIONALE
Transcutaneous electrical stimulation (ES) consists of delivering small electrical pulses via electrodes that are positioned on the skin, usually around skeletal muscle motor points or painful body areas. Depending on electrical current (frequency and intensity) and electrode characteristics (size, position), two major ES categories can be distinguished:
- ‘Sensory’ ES (no muscular contractions are evoked). Conventionally called transcutaneous electrical nerve stimulation. This is mainly delivered using relatively low current intensities (at or below the sensory threshold) in an attempt to relieve pain via spinal circuitry transmitting pain (gate theory) and endorphin release.
- ‘Motor’ ES. Conventionally called neuromuscular electrical stimulation. This elicits visible muscular contractions (stimulations are delivered at or above the motor threshold), using either tetanic or sub-tetanic stimulations, whose clinical/physiological consequences are improved neuromuscular function and enhanced peripheral blood flow.
In reality, this distinction is not always respected and considerable confusion continues to surround the main physiological effects, methodological aspects and clinical/sports applications of transcutaneous ES.
Some individual and team sport athletes use motor ES modalities as a complement to their training/rehabilitation programmes for:
- improving muscle strength during the pre-season,
- maintaining/improving muscle function while injured/after an injury and
- restoring physical performance after intense exercise (i.e. for accelerating recovery).
There is some evidence to suggest that motor (tetanic) ES is effective to increase muscle strength in athletes (for a review see Seyri and Maffiuletti1), and to preserve muscle mass during prolonged periods of inactivity2. Surprisingly, however, the growing interest in applied research on tetanic ES observed in the last few years has corresponded to a reduced use by athletes and reduced development by manufacturers. At the same time, but with premature physiological background, subtetanic ES has gained popularity in sportspeople as a potentially effective strategy to accelerate post-exercise recovery.
This review article aims to assess the effectiveness of motor subtetanic and sensory ES as a recovery modality for athletes by following a simplified and non-systematic approach. Because the post-exercise decline in physical/sports performance is due to an impairment in neuromuscular and/or psychomotivational function, and because recovery modalities are designed to restore neuromuscular function and/or psychomotivational function to the pre-exercise level as quickly as possible, we preferred to provide separate definitions, analyses and interpretations for ‘physiological’ and ‘perceptual’ recovery throughout the article. We therefore considered original research studies:
- published in peer-reviewed journals,
- comparing the effectiveness of ES-related recovery strategies to passive recovery or other recovery modalities (at least two conditions),
- focusing on athletes or healthy subjects,
- having quantified at least one physiological and/or perceptual variable of recovery.