Prolonged static stretching causes acute, non-metabolic fatigue and impairs exercise tolerance during severe intensity cycling

We tested the hypothesis that static stretching, an acute, non-metabolic fatiguing intervention, reduces exercise tolerance by increasing muscle activation and affecting muscle bioenergetics during cycling in the "severe" intensity domain. Ten active men (24±2 years, 74±11 kg, 176±8 cm) repeated an identical constant load cycling test, two tests were done in control conditions and two after stretching, that caused a 5% reduction of maximal isokinetic sprinting power output. We measured: i) oxygen consumption (VO2); ii) electromyography: iii) deoxyhemoglobin iv) blood lactate ([La-]); v) time to exhaustion (TTE) vi) perception of effort. Finally, VO2 and deoxyhemoglobin kinetics were determined. Force reduction following stretching was accompanied by augmented muscle excitation at a given workload (p=0.025), and a significant reduction in TTE (p=0.002). The time to peak of VO2 was reduced by stretching (p=0.034), suggesting an influence of the increased muscle excitation on the VO2 kinetics. Moreover, stretching was associated with a mismatch between O2 delivery and utilization during the on-kinetic, increased perception of effort and [La-], that are all compatible with an increased contribution of the glycolytic energy system to sustain the same absolute intensity. These results suggest a link between exercise intolerance and the decreased ability to produce force. Novelty bullets: • We provided the first characterization of the effects of prolonged stretching on the metabolic response during severe cycling. • Stretching reduced maximal force, augmented muscle activation in turn increasing the metabolic response to sustain exercise.