One long vs. two short sessions? Physiological and perceptual responses to low-intensity training at self-selected speeds in cross-country skiers

Background Cross-country skiers perform ~90% of their endurance training volumes as low-intensity training (LIT)1, although the underlying mechanisms of LIT are relatively unexplored in the scientific literature. The present study compared self-selected speeds and corresponding physiological responses and perceived training stress between one long session vs. two shorter sessions of LIT in one day among skiers. Methods Thirteen national-level male skiers performed two different LIT types during classical rollerskiing matched for the same distance in a counterbalanced order. The training consisted of either one long (~3 hours) session (1LIT) or two shorter (~1.5 hour each) sessions (2LIT) with 7 hours of recovery in between. Speed, heart rate (HR), rating of perceived exertion (RPE), and blood lactate (Bla) were measured, and perceived training stress assessed after sessions. Results 2LIT was performed at 1.9±2.0% higher speeds vs. 1LIT (P≤0.01). Higher speeds were also found in the second vs. first session of 2LIT and the second vs. first part of 1LIT (1.9±3.2% and 3.2±3.6%, respectively, both P≤0.01). There were no significant differences between LIT types in HR, although RPE increased in the second vs. first part of 1LIT (0.9±0.8-point P≤0.01). Bla was reduced in the second vs. first session/part of both LIT types (~0.16±0.20 mmol·L-1, P≤0.05). Higher perceived muscular exertion (2.0±1.1-point P≤0.01) was found directly after 1LIT. Conclusions Compared to a distance-matched long session, skiers perform two shorter sessions of LIT at slightly higher self-selected speeds with the same physiological responses elicited although minor differences in perceived training stress were observed