Does increasing intensity reduce the rate of nonresponders to endurance training when total energy expenditure remains constant?

Abstract Background Standardized training prescriptions often result in large variation in training response with a substantial number of individuals that show little or no response at all. The present study examined whether the nonresponse in markers of cardiorespiratory fitness (CRF) to moderate intensity endurance training can be overcome through an increase in training intensity. Methods Thirty-one healthy, untrained participants (46 ± 8 years, BMI 25.4 ± 3.3 kg•m-2 and V̇O2max 34 ± 4 mL•min-1•kg-1) trained for 10 weeks with moderate intensity (3 d•wk-1 for 50 min per session at 55% HRreserve). Hereafter, the allocation into two groups was performed by stratified randomisation for age, gender and VO2max response. CON trained for another 16 weeks at moderate intensity, INC trained energy-equivalent for 8 weeks at 70% HRreserve and then performed high-intensity interval training (4x4) for another 8 weeks. Nonresponders were identified as participants with VO2max increase below the technical measurement error. Results There was a significant difference in V̇O2max response between INC (3.4±2.7mL•kg-1•min-1) and CON (0.4±2.9 mL•kg-1•min-1 ) after 26 weeks of training (P=.020). After 10 weeks of moderate training, in total 15 of 31 participants were classified as VO2max nonresponders (48%). After another 16 weeks continuous moderate intensity training, no further reduction of nonresponders was observed in CON. In contrast, the energy equivalent training with increasing training intensity in INC significantly (P=.008) reduced the number of nonresponders to 2 of 15 (13%). The energy equivalent higher training intensities eliminated the rate of nonresponders more effectively than continued moderate training intensities (P=.012). Conclusion Increasing exercise-intensity can reduce the rate of nonresponse in VO2max to endurance training even when the total energy expenditure is held constant. Maintaining moderate endurance training intensities might not be the best choice to optimize training gains.