Comparison of training intensities for optimal endurance running performance

Summary:
Introduction: A cluster of studies in the sport science literature employ interval training (alternating bouts of recovery and rest periods) interventions for the purpose of identifying optimal training intensities for endurance performance. There has been evidence to support the likelihood that among the most optimal training stimuli are two specific intensities: the velocity associated with the maximal rate of oxygen uptake (v 2max); and the intermediate velocity between v 2max and the velocity associated with the lactate threshold (vΔ50). It has not been shown to date, which of the two interval training intensities (v 2max or vΔ50) enhances performance and laboratory determined performance-related parameters the most, when applied in a complete yearly training cycle of endurance runners. Most studies have been too short to provide definitive answers.
Aim of the study: The aim of the study was to compare the interval training intensities v 2max and vΔ50 in a complete yearly training cycle so as to generate evidence as to which of the two impacts performance and performance-related parameters the most, with the goal of providing new knowledge in sport science.
Methods: 32 out of the 45 male runners recruited initially completed the whole duration of the study (mean ± SD: body mass 72.0±8.0 kg, body height 175±6 cm, body fat 9.9±3.9 %, 2max 53.6±6.2 ml/kg.min, age 34±12 years). Subjects underwent a 20-week aerobic base of preparatory training (at an intensity equivalent to a rate of perceived exertion (RPE) of 10.4 to 11.0) and anaerobic threshold training (at an intensity equivalent to an RPE of 14.5 to 15.0). No high intensity training was included. At the end of the aerobic phase the runners underwent a pre-test phase for the determination of vΔ50, v 2max, 2max, vLT4 (speed associated with a lactate concentration of 4 mmol/L), ECR (Energy Cost of Running) and Tmax (maximum time at v 2max) in the laboratory and 1500-m and 5000-m time trial (TT) times on the track. The subjects were randomly assigned into one of two groups before entering the 16-week interval training intervention phase. The only difference between the two groups was the intensity of the interval training. Group A (n = 15) was trained at a heart rate associated with vΔ50 (mean RPE 16.8 to 17.0) and Group B (n = 17) was trained at a heart rate associated with v 2max (mean RPE 18.6 to 18.7). At the end of the interval training phase the subjects underwent the post-test phase involving the same tests as during pre-testing. A 2X2 (time VS. interval training intensity) mixed model analysis of variance was used to test for significant differences between and within groups and the level of significance was set at p< 0.05.
Results: Group A improved significantly (mean difference and Confidence Interval (CI)) in 1500-m TT (10.1 s, CI 5.6 to 14.7 s), in 5000-m TT (22.9 s, CI 9.6 to 36.3 s), in vΔ50 (-0.4 km/h, CI -0.8 to -0.1 km/h), in Tmax (-71 s, CI -113 to -28 s) and vLT4 (-0.5 km/h, CI -0.8 to -0.1 km/h). Group B improved significantly (mean difference and CI) in 1500-m TT (11.7 s, CI 7.5 to 15.9 s), in 5000-m TT (29.0 s, CI 16.5 to 41.5 s), in vΔ50 (-0.4 km/h, CI -0.7 to -0.1 km/h), in v 2max (-0.4 km/h, -0.7 to -0.01 km/h) in Tmax (-78 s, CI -114 to -42 s) and in ECR (0.013 ml/m/kg, CI 0.005 to 0.021 ml/m/kg). Regression analyses showed that v 2max and vΔ50, individually, accounted for the highest degree of variance in 1500-m TT times (77% and 69%, respectively) and 5000-m TT times (79% and 78%, respectively). During multiple regression analyses v 2max was likely to be the most important predictor in the regression models predicting 1500-m TT times and vΔ50 was the most important predictor in the regression models predicting 5000-m TT times.
Conclusions: The interval training intensities v 2max and vΔ50 were significant in leading to endurance performance improvement as well as to improvement in some associated physiological parameters. The novel findings were that, a) it was demonstrated that vΔ50 was significant in inducing improvements in the 1500-m TT, b) that both v 2max and vΔ50 may be the most important predictors of 1500-m and 5000-m performance in regression analyses and that, c) v 2max and vΔ50 may, with a high degree of probability, be the most important predictor of 1500-m and 5000-m times, respectively, during multiple regression analyses. The evidence seems to weigh towards v 2max to be a slightly more optimal training stimulus than vΔ50, which also constitutes an important training intensity. Considering injury potential, repetitive stress on the athletes and optimal training it may be that a combination may be sensible.