GAS-EXCHANGE AND NEUROHUMORAL RESPONSE TO EXERCISE - INFLUENCE OF THEEXERCISE PROTOCOL

Maximal oxygen uptake varies with the exercise protocol, but the exten t to which hormonal and metabolic responses to exercise are influenced by the exercise protocol has not been precisely defined. Twelve healt hy subjects underwent maximal exercise testing using two incremental b icycle tests with individualized, identical work rate increments betwe en 40 and 70 W. One protocol employed a 1-min and the other a 3-min du ration per stage. Expiratory gas and venous blood were sampled at regu lar intervals for metabolic and hormonal analysis. Exercise duration f or the 1-min and 3-min protocols was 6.0 +/- 0.1 and 14.3 +/- 0.3 min, respectively (P < 0.001). Significantly higher values were observed f or peak VO2 and maximal ventilation during the 3-min protocol compared with the 1-min protocol (41.1 +/- 1.8 vs 38.3 +/- 1.6 ml.kg(-1).kg(-1 ).min(-1), P < 0.001; and 104.9 +/- 8.0 vs 97.2 + 5.7 l.min(-1), P < 0 .05, for peak VO2 and peak ventilation, respectively). However, the ma ximal workload achieved was higher during the 1-min versus the 3-min p rotocol (300 + 24 vs 280 + 21 W, P < 0.01). No differences were observ ed for maximal heart rate or blood pressure, whereas maximal plasma la ctate was roughly twice as high during the 3-min compared with the 1-m in protocol (7.5 +/- 0.8 vs 3.8 +/- 0.5 mmol.l(-1), P < 0.001). Norepi nephrine, epinephrine, dopamine, and growth hormone levels were genera lly higher throughout exercise during the 3-min compared with the 1-mi n protocol. When expressed as a percentage of peak VO2, however, diffe rences in catecholamine levels were not observed. Endothelin levels di d not change. We conclude that the exercise protocol profoundly influe nces exercise capacity as well as the metabolic and hormonal response to exercise and should be considered when using these variables to eva luate an intervention.