Physiological responses to repeated bouts of high-intensity ultraendurance cycling--a field study case report

The present study aimed to 1) examine the relationship between laboratory-based measures and high-intensity ultraendurance (HIU) performance during an intermittent 24-h relay ultraendurance mountain bike race (∼20 min cycling, ∼60min recovery), and 2) examine physiological and performance based changes throughout the HIU event. Prior to the HIU event, four highly-trained male cyclists (age= 24.0±2.1 yr; mass= 75.0±2.7 kg; V̇O2peak= 70±3 ml·kg -1·min-1) performed 1) a progressive exercise test to determine peak volume of oxygen uptake (V̇O2peak), peak power output (PPO), and ventilatory threshold (Tvent), 2) time-to-fatigue tests at 100% (TF100) and 150% of PPO (TF150), and 3) a laboratory simulated 40-km time trial (TT40). Blood lactate (Lac -), haematocrit and haemoglobin were measured at 6-h intervals throughout the HIU event, while heart rate (HR) was recorded continuously. Intermittent HIU performance, performance HR, recovery HR, and Lac- declined (P<0.05), while plasma volume expanded (P< 0.05) during the HIU event. TF100 was related to the decline in lap time (r= -0.96; P< 0.05), and a trend (P= 0.081) was found between TF150 and average intermittent HIU speed (r= 0.92). However, other measures (V̇O 2peak, PPO, Tvent, and TT40) were not related to HIU performance. Measures of high-intensity endurance performance (TF 100, TF150) were better predictors of intermittent HIU performance than traditional laboratory-based measures of aerobic capacity.