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

This study examined die 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-(V) over dotO(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-(V) over dot O-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% (V) over dot O-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 center dot 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 center dot 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), a] though 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 dian the same amount of intermittent exercise undertaken with a short work-rest duration.