Adaptive Functional Electrical Stimulation Kinesitherapy added to cycling boosts plasma irisin levels.

Although the impact of endurance training on irisin levels has been widely investigated in the past decade,1,2,3 no studies have examined the response of this myokine to endurance training with percutaneous Neuromuscular Electrical Stimulation (NMES). The study compared the acute irisin response to cycling with and without a novel technology Adaptive Functional Electrical Stimulation Kinesitherapy (AFESK™) delivered through the VIK8 device (AFESK™ technology, VIK8, VIKTOR S.r.l., Italy) at both the beginning and end of a 6-week training period (14 sessions), aiming to examine the additional load of AFESK and assess potential adaptation effects. Sixteen active male participants (age 39 ± 10 years, O2peak 48.0 ± 4.8 ml·min·Kg-1) were randomly allocated to two groups and matched for O2peak and age. The cycling (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 cycling with C + AFESK group did the same training program using the VIK8 device to deliver AFESK on lower limbs muscles. Irisin response was evaluated before and after (15m, 24h, 48h post) the first (S1) and the last training session (S14). Irisin plasma concentration was detected by ELISA assay. Timepoint x Group repeated measures ANOVA and Wilcoxon signed-rank test were used for statistical analyses. Both C and C+AFESK caused significant increases in irisin levels (p<0.001) from baseline (S1, C: 7.3±1.7 ng/ml, C+AFESK: 8.2±1.5 ng/ml; S2, C: 7.3±1.5 ng/ml, C+AFESK: 8.6±1.5 ng/ml) peaking at 24h (S1, C: 9.9±1.3 ng/ml, C+AFESK: 11.8±1.6 ng/ml; S2, C: 10.0±1.0 ng/ml, C+AFESK: 13.0±1.6 ng/ml) and returning to baseline after 48h (S1, C: 7.2±1.7 ng/ml, C+AFESK: 8.1±1.5 ng/ml; S2, C: 7.3±1.4 ng/ml, C+AFESK: 8.7±1.5 ng/ml). Before and after the training period, concentration of irisin in the C+AFESK group was significantly more elevated than in the C group 24h post-exercise (S1, p<0.05; S2, p<0.001). No significant changes in baseline concentration were observed in both groups, however, after 6 weeks of training, the irisin quantity from baseline to 24h (expressed as delta) increased significantly in the C+AFESK (from 3.6±0.4 to 4.4±0.5 ng/ml, p<0.05) and remained unchanged in the C group (from 2.6±0.8 to 2.6±0.8 ng/ml). AFESK during cycling led to a greater release of irisin one day after exercise compared to traditional cycling. The training period, with or without AFESK, does not appear to affect baseline irisin levels. The AFESK, by delivering the electrical stimulus in synchrony with the voluntary contraction of the targeted skeletal muscle, may further enhance irisin release relative to normal cycling training, providing valuable insights into the mechanisms underlying irisin secretion.