The effects of work-rest duration on intermittent exercise and subsequent performance

This study examined the effects of different work-rest durations during 40 min intermittent treadmill exercise and subsequent running performance. Eight males (mean ± s: age 24.3 ± 2.0 years, body mass 79.4 ± 7.0 kg, height 1.77 ± 0.05 m) undertook intermittent exercise involving repeated sprints at 120% of the speed at which maximal oxygen uptake (v-V̇O_2max) was attained with passive recovery between each one. The work-rest ratio was constant at 1:1.5 with trials involving short (6:9 s), medium (12:18 s) or long (24:36 s) work-rest durations. Each trial was followed by a performance run to volitional exhaustion at 150% v-V̇O_2max. After 40 min, mean exercise intensity was greater during the long (68.4 ± 9.3%) than the short work-rest trial (54.9 ± 8.1% V̇O_2max; P < 0.05). Blood lactate concentration at 10 min was higher in the long and medium than in the short work-rest trial (6.1 ± 0.8, 5.2 ± 0.9, 4.5 ± 1.3 mmol·l^-1, respectively; P < 0.05). The respiratory exchange ratio was consistently higher during the long than during the medium and short work-rest trials (P < 0.05). Plasma glucose concentration was higher in the long and medium than in the short work-rest trial after 40 min of exercise (5.6 ± 0.1, 6.6 ± 0.2 and 5.3 ± 0.5 mmol·l^-1, respectively; P < 0.05). No differences were observed between trials for performance time (72.7 ± 14.9, 63.2 ± 13.2, 57.6 ± 13.5 s for the short, medium and long work-rest trial, respectively; P = 0.17), although a relationship between performance time and 40 min plasma glucose was observed (P < 0.05). The results show that 40 min of intermittent exercise involving long and medium work-rest durations elicits greater physiological strain and carbohydrate utilization than the same amount of intermittent exercise undertaken with a short work-rest duration.