A calorimetric analysis of eccentric and concentric bicycle ergometry

Farrell, Robert Thomas Christopher (1986) A calorimetric analysis of eccentric and concentric bicycle ergometry. Masters thesis, Memorial University of Newfoundland.

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Abstract

Phase I of this study entailed a verification of the relationship between oxygen consumption and both concentric and eccentric workrate on the bicycle ergometer constructed for the whole body human calorimeter. This series of exercise experiments, carried out without calorimetry, included a range of pedaling speeds and brakeforces, but also “idling”, i.e. pedaling only against the frictional resistance of the ergometer transmission and passively “being pedaled” by the electric motor of the eccentric exercise ergometer. It also included experimentation with the brake on the flywheel, by substituting the von Döblen brake on the monarch ergometer by a known weight suspended from the brake belt. Only one subject was employed for the total of 36 experiments. -- Phase II was carried out on six subjects, who performed a total of 79 experiments with concentric and eccentric exercise at a range of pedaling speeds and brakeforces in the calorimeter. All experiments were carried at a calorimeter temperature of 32.36 + 0.06°C and a dew point temperature of less than 6°C. Each experiment lasted about 50 minutes, or until the various monitored variables, sensible and insensible heat exchange, heart rate and body core temperature (tympanic or esophageal) showed a steady state as judged by visual inspection. Immediately prior to this state metabolic heat production was determined in duplicate from the measurement of oxygen consumption and respiratory quotient. Near the end of the experiment the subject reported his perceived exertion on the Borg scale. -- Phase I, which was intended to familiarise the author with the various methods, did not reveal anything that was not yet known from the current literature. The net mechanical efficiency of exercising on the calorimeter ergometer was 18.6% for concentric work and -100.4% for eccentric work. There was little to be gained by modifying the braking mechanism. -- In Phase II the energy balance was analysed by adding algebraically all heat gains and heat losses during the apparent caloric and thermal steady state. Surprisingly, there was usually a small positive heat storage which was most closely related to the concentric or eccentric workrate applied, and to ta lesser extent to the metabolic heat production. -- Conclusions -- 1. With direct calorimetry one can detect rates of heat storage which cannot be detected by thermometry at the conventional body sites. After 50 minutes of continuous exercise, either concentric or eccentric, there was a small amount of heat storage, which was associated with the workrate (0.5 W storage per applied workrate in watts), but not with metabolic heat production. The average heat storage was small at 33 watts for all experiments. A heat storage rate of 33 watts converts, in a 70 kg subject, to a rise in average body temperature of 0.008°C/min. This may well go undetected by observing the eardrum and mean skin temperature, if the storage takes place in peripheral body regions such as the exercising muscle. -- 2. It is not possible to quantitate internal work thermodynamically as the energy required to overcome these forces must ultimately be derived form aerobic metabolism and thus would show up as heat.

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