Five Weeks of Sprint Interval Training Increase Absolute Power Output Within Severe-Intensity Domain Without Altering Muscle Activation or Fatigability

The study aimed to investigate whether a 5-week sprint interval training (SIT) could improve neuromuscular function (NMF), alter electromyographic activity (EMG), and attenuate fatigability, ultimately resulting in improved cycling performance during constant work rate (CWR) exercise within the severe-intensity domain. Twenty-one recreational active males were randomly assigned into a SIT group (SIT_G; n = 11) that underwent 5 weeks of SIT (4–6, 30-s Wingate bouts) and a control group (CON; n = 10). The study was conducted in a parallel independent group study. At the pre- and post-training periods, participants performed (i) a ramp incremental test; (ii) CWR exercise at 150% of the pre- and post-training power output at the respiratory compensation point (RCP-PO) until task failure, with the NMF assessed at baseline (NMF_BL) and immediately after exercise [isometric maximal voluntary contraction + peripheral nerve stimulations with measurement of the force and EMG]. Pre- and post-training NMF_BL was used to assess isometric performance, whereas the difference between NMF_BL and NMF after exercise was used to assess performance fatigability. Furthermore, EMG was also measured during exercise. SIT_G showed a significant increase in absolute RCP-PO compared to CON (+11.0% vs. −0.7%, respectively; p < 0.01), performing the post-training CWR at a greater power output than in pre-training. Despite this, no significative differences were observed for the NMF_BL, fatigability, and EMG during CWR exercise. These findings suggest that SIT may improve EMG activity efficiency (i.e., requiring the same level of activation to sustain a greater absolute power output) during CWR exercise within the severe-intensity domain. However, NMF_BL, fatigability, and time-to-task failure performance remained unchanged.