Does low-intensity endurance training improve endurance capacity as effectively as moderate-intensity training when total energy expenditure is held constant in healthy untrained subjects?
Low-intensity endurance training may be slightly less effective than moderate-intensity training for improving oxygen uptake at the anaerobic threshold, even when total energy expenditure is matched.
Recent studies point to the preventive efficacy of low-intensity endurance training in terms of cardiovascular risk factor modification and mortality reduction. In addition, it is frequently recommended as a means of stimulating fat metabolism. It was the intention of this study to clarify if endurance training effectiveness remains unimpaired when exercise intensity is reduced by a certain amount from "moderate" to "low", but total energy expenditure held constant. For this purpose, 39 healthy untrained subjects (44 +/- 7 yrs, 82 +/- 19 kg; 173 +/- 9 cm) were stratified for endurance capacity and sex and randomly assigned to 3 groups: "moderate intensity" (MOD, n = 13, 5 sessions per week, 30 min each, intensity 90 % of the anaerobic threshold baseline lactate + 1.5 mmol/l), "low intensity" (LOW, n = 13, 5 sessions per week, intensity 15 bpm below MOD, duration proportionally longer to arrive at the same total energy output as MOD), and control (CO, n = 13, no training). Training was conducted over 12 weeks and each session monitored by means of portable heart rate (HR) recorders. Identical treadmill protocols prior to and after the training program served for exercise prescription and documentation of endurance effects. VO (2max) improved similarly in both training groups (MOD + 1.5 ml x min (-1) x kg (-1); LOW + 1.7 ml x min (-1) x kg (-1); p = 0.97 between groups). Compared with CO (- 1.0 ml x min (-1) x kg (-1)) this effect was significant for LOW (p < 0.01) whereas there was only a tendency for MOD (p = 0.07). However, objective criteria (HR (max), maximal blood lactate) indicated that a different degree of effort was responsible for this finding. In comparison with CO (mean decrease of 3 bpm), average HR during incremental exercise decreased significantly by 9 bpm (MOD, p < 0.05 vs. CO) and 6 bpm (LOW, p = 0.26), respectively. However, there was no significant difference between MOD and LOW (p = 0.60), but for changes in oxygen uptake at the anaerobic threshold (VO (2AT)) it was observed that MOD was significantly more effective than CO (p = 0.048) and LOW (p = 0.04). It is concluded that within a middle-aged population of healthy untrained subjects, endurance training effectiveness might be slightly impaired when the training heart rate is chosen 15 bpm lower as compared to moderate intensity, but the total energy output held equal.
Meyer et al. (Mon,) studied this question.