The effects of pedaling exercise with superimposed adaptive functional electrical stimulation (AFESK) on the physiological and perceptual responses to exercise and performance in healthy humans: a training study.

Percutaneous Neuromuscular electrical stimulation (NMES) is a well-known methodology used in sports medicine both for strength training and rehabilitative issues (1). Recently, the effects of NMES during pedaling exercise have been investigated, suggesting a higher metabolic and cardiorespiratory response compared to a control condition that might enhance training effects (2). Despite this, training studies failed to show a higher effectiveness of this method compared to normal cycling (3). One of the reasons might be ascribed to the time asynchrony between NMES and voluntary contraction. The aim of this pretest-posttest training study (6 weeks period/ 2-3 sessions per week) was to investigate the effects of a novel technology Adaptive Functional Electrical Stimulation Kinesitherapy (AFESK™) delivered through the VIK8 device (AFESK™ technology, VIK8, VIKTOR S.r.l., Italy) that can trigger the electrical stimulus in synchrony with the voluntary contraction of the stimulated muscle. Sixteen active male participants (age 39 ± 10 years, VO2peak 48.0 ± 4.8 ml·min·Kg-1) were randomly allocated to two groups. The control (C) group performed 4x5m intervals at 60% peak power output [PPO] (achieved during an incremental test to exhaustion) interspersed with 3m recovery at 40% PPO. The experimental (EXP) group did the same training program superimposing AFESK on lower limbs muscles during all the training sessions. Before and after the training period, aerobic and anaerobic lactate thresholds, cardiorespiratory and perceptual responses to incremental step (5 min) exercise, maximal power output for 6 seconds sprint, performance (5 km time trial) were assessed during cycling. Similarly, the neuromuscular function of the knee extensors muscles (NMF) was investigated in isometric conditions. Change scores between post and pre assessments were determined in each group and for each dependent variable. Change scores between groups were compared using Mann- Whitney U test. Data are presented as mean ± standard deviation. Power outputs at aerobic (CON +4 ± 19 W vs EXP +27 ± 22 W, p = 0.031) and anaerobic (CON +1 ± 14 W vs EXP +28 ± 23 W, p=0.021) lactate thresholds statistically increased in EXP. Heart rate and perception of effort remained stable in both groups (all p values > 0.05). Similarly, during the incremental step exercise at the cycle ergometer none of the dependent variables ( O2, CO2, RER, e, Bf) changed (all p values > 0.05). During the 6 seconds sprint cycling, mean power output statistically (p = 0.028) increased in EXP (+26 ± 29 W) but not in CON (-3 ± 23 W), while peak power output (CON +3 ± 44 W vs EXP 29 ± 37 W, p = 0.372) was unchanged in both groups. The 5 km total time did not statistically change (CON +1 ± 15 s vs EXP -8 ± 8 s, p = 0.226). The training period did not impact on maximal voluntary contraction (CON -1 ± 45 Nm vs EXP -8 ± 30 Nm, p = 1.000) and activation levels (CON -1 ± 4 % vs EXP +3 ± 6 %, p = 0.161) but reduced evoked twitch at 1 Hz (CON +3 ± 6 Nm vs EXP -2 ± 4 Nm, p = 0.038) and 100 Hz (CON +4 ± 9 Nm vs EXP -7 ± 7 Nm, p = 0.038). Using AFESK during cycling for a period of 6 weeks seems to increase the power output at the Aerobic (2 mmol/l b[La]) and Anaerobic (4 mmol/l b[La]) thresholds more than normal training; this occurred with unaltered physiological and perceptual responses to exercise (Pre – Post training period) in both groups. Furthermore, mean power output during 6 seconds cycling sprint at the cycle ergometer seems to increase only in EXP. The mechanical response of the quadriceps muscle to a single and a double twitch (100 Hz), measured after the training period, seems to decrease in EXP (likely higher fatigue). Changes in power output at the aerobic and anaerobic thresholds might be partly ascribed to a small higher level of muscle strain caused by the administration of AFESK.