The influence of nutritional interventions on the measurement of gross efficiency during cycling

Many research studies report and monitor cycling efficiency over a sustained period of time. None of these studies report that the nutritional intake was controlled or recorded across the period of assessment.

PURPOSE: To determine whether manipulation of nutritional intake before, during and after cycling exercise could influence subsequent gross efficiency measurement.

METHODS: Thirty six cyclists were split into three groups and undertook one of three studies. All studies involved repeated 2-hour cycling tests at submaximal exercise intensity (60% of Power at V̇O2max) in a randomised, crossover design. During study A, carbohydrate (CHO) intake was manipulated in the 3-days preceding cycling trials. Participants consumed isocaloric diets (~4000kcal) that contained a high (70%), moderate (45%) or low (20%) proportion of CHO, with the remaining proportions derived from fat and protein (10%) intake. For study B, cyclists consumed a standard 3-day pre-exercise diet and conducted four exercise tests where they consumed water (600ml.h-1), CHO (36g.h-1), caffeine (5mg.kg-1) or both CHO and caffeine in combination during the test. During study C, cyclists undertook four exercise trials. Following a standard 3-day pre-exercise diet, participants completed the first two tests on consecutive days and consumed either a high or a low CHO diet (identical to study A) in the 24-h period between tests. A week later, this was repeated with the alternative diet ingested in the recovery period between trials. During all tests, expired air was measured at 30 min intervals in order to calculate gross efficiency (GE).

RESULTS: A – GE was significantly greater following the High CHO diet than the Mod CHO diet. (HighCHO=20.1 ± 0.5%, ModCHO=19.3 ± 0.6%, mean ± SD; P<0.05). B - The decline in GE over time was significantly lower after the ingestion of CHO (Water=-1.8 ± 1.1%, CHO=-0.7 ± 0.1%; P<0.05). C - Dietary intervention did not alter GE (HighCHO =19.5± 0.2%, LowCHO 19.2± 0.4%; P>0.05).

CONCLUSION: Significant differences in gross efficiency were obtained following alteration of nutritional intake in the 3-days preceding and during exercise. This suggests that nutritional intake should be carefully controlled and monitored to ensure the validity of gross efficiency measurements.