Optimising Endurance Training of Elite Cyclists by Inclusion of Sprints During Low-Intensity Sessions

Competitive cycling at the elite level is a demanding endurance sport with up to 300 km long races. Elite cyclists annually spend up to ~1000 hrs on the bike, with the majority of training time spent as low-intensity training (LIT) and only ~2-10% in the high-intensity domain (i.e., above the second ventilatory threshold). The decisive moments of cycling (e.g., to establish a break-away or to sprint for the finish line), involve maximal efforts, and top-10 finishers have higher short (<5 min) power outputs, compared to non-top-10 finishers. However, further increasing HIT-load to improve these competition-specific abilities may increase the risk of overreaching and burnout. Sprint training could be an alternative to this, but dedicating entire training sessions to e.g., sprint training might not be a time-efficient strategy. Therefore, including 30-s sprints during LIT-sessions could be an alternative to improve performance (i.e., sprint and endurance performances) after prolonged exercise, which are specific for road races. The aims of this thesis were first, to investigate the acute responses to inclusion of 30-s maximal sprints during a LIT-session (Paper I and II), and second, to investigate adaptations to repeated inclusion of sprints during LIT-sessions in periods of habitual changes in total training load (Paper III and IV). This was studied in three consecutive studies, outlined in four separate papers.
In Papers I and II, we investigated the effects of including sprints during a 4-h LIT-session on acute physiological responses, the subsequent muscular and hormonal responses, as well as the recovery of muscle strength in the following 24 hrs. The effects of including sprints (SPR) were compared to a work-matched LIT-session (CON) in a randomized cross-over design on 12 elite cyclists (maximal oxygen uptake, VO2max: 73±4 mL·kg-1·min-1). In Paper I, SPR temporarily changed pedalling technique and muscle activity patterns but did not affect the overall change in gross efficiency (GE) during prolonged cycling, which decreased ~1%-point during the 4-h session in both SPR and CON. Also, repeated sprint performance was maintained during prolonged cycling in SPR. In Paper II, SPR induced more pronounced changes in mRNA levels of markers of fat metabolism (­PDK4), angiogenesis (­VEGFA), protein turnover (­MuRF1 and ̄Myostatin), ion transport ( ̄Na+-K+a1, ̄CLC1, and ̄NHE1) and mitochondrial biogenesis ( ̄PGC-1a) in m. Vastus lateralis compared to CON. Hormonal responses to a LIT-session of habitual duration were overall small in elite cyclists and similar in SPR and CON. However, SPR induced lower responses of growth hormone and sex hormone-binding globulin compared to CON, indicating a generally low endocrine stress response. Importantly, recovery of muscle strength (isokinetic knee extension) was completed 24 hrs after both conditions.
In Paper III and IV, the adaptations to inclusion of sprints during LIT-sessions were investigated in two ~3-wk interventions of habitual changes in total training load in elite cyclists. In Paper III, the effects of including sprints during one weekly LIT-session (SPR, n=7, VO2max: 73±5 mL·kg-1·min-1) compared to only LIT (CON, n=9, VO2max: 71±5 mL·kg-1·min-1) during a 3-wk transition period of ~60% reduced training load were investigated. Here, SPR improved 30-s sprint mean power 8% more than CON. In addition, after the ~2-h exercise test, 20-min power and fractional utilization of VO2max (%VO2max) were maintained in SPR, while CON reduced these variables, but was not different from SPR. Inclusion of sprints did not affect power output at 4 mmol·L-1 [BLa-] (L4), which was equally reduced in both groups. However, VO2max, maximal aerobic power (Wmax), and mental recovery (total burnout) were not affected by the substantially reduced training load in any of the groups.
In Paper IV, the effects of including sprints (SPR, n=9, VO2max: 75±5 mL·kg-1·min-1) on 5 LIT-sessions during a 14-d training camp, followed by a 10-d recovery period, compared to LIT only (CON, n=9, VO2max: 75±5 mL·kg-1·min-1) were investigated. The training load was increased and decreased by ~50%, respectively, compared to habitual training. SPR improved 30-s sprint and 5-min mean power ~4% more than CON, without affecting total mental stress/recovery. In addition, SPR
Summary
maintained protein abundancy of Na+-K+b1 and GE, while Na+-K+b1 was reduced 8% more in CON and GE was reduced after prolonged exercise only in CON. SPR tended to improve %VO2max during the 5-min test after prolonged exercise, but was not different to CON. However, neither power output and %VO2max at L4, VO2max, nor Wmax were affected by the addition of sprints or by the substantial changes in training load.
In summary, inclusion of sprints during a prolonged LIT-session did not change GE compared to LIT only, but potentially leads to beneficial adaptations in skeletal muscle without impairing muscular performance on the following day. When elite cyclists included a small number (27-51) of sprints during LIT-sessions, 30-s mean power was improved by 4% to 8% more than LIT only, irrespectively of substantial changes in total training load. Furthermore, inclusion of sprints maintained 20-min performance in periods of decreased training load and improved 5-min performance in periods of increased training load, without affecting burnout or mental stress/recovery. The addition of sprints primarily affected performance-related measures after prolonged exercise, whereas measures in the fresh state (e.g., power output at L4, VO2max and Wmax) were not altered by sprinting. It is, therefore, suggested that sprints can be included in habitual LIT- sessions to improve competition-specific performance of elite cyclists without affecting mental stress/recovery or increasing the risk of burnout.