Relationship between body composition, blood volume and maximal oxygen uptake

Abstract

SummaryIt has long been known that body mass and, more specifically, lean body mass are strongly correlated with maximal oxygen uptake (VO 2max ) in man and animals. However, there are no data to date describing this phenomenon in the horse. The purpose of this paper is to examine the relationship between body composition and VO 2max in the horse. Twenty-three healthy and unfit Standardbred mares performed an incremental exercise test (GXT) to measure VO 2max . Rump fat thickness (RTH), a measure of fat covering, was measured using B-mode ultrasound. Plasma volume, total blood volume and red cell volume were determined, using the Evan's Blue dye dilution technique and packed cell volume. VO 2max was correlated with body mass (r = 0.541; P<0.01) and exercise haematocrit (exHCT; r = 0.407; P<0.05) but not RTH or the other haematological variables. To eliminate the influence of body mass on the individual variables, a regression analysis was performed on the mass-residuals of VO 2max , RTH, plasma volume and exHCT. The residuals of VO 2max were correlated negatively with the residuals of RTH (r = -0.687; P = 0.0003) and positively with the residuals of exHCT (r = 0.422; P = 0.045) but not plasma volume. VO 2max could be predicted from a linear combination of the residuals of RTH and exHCT (r = 0.767; P<0.0001). These data indicate that VO 2max in the horse is significantly related to fat-free mass (FFM), independent of body mass. Red blood cells from the splenic reserve constitute an important factor in the horse's ability to achieve a high VO 2max . Therefore, lean body mass may be a more appropriate basis for assessing metabolic function in the athletic horse. IntroductionThe horse is an 'elite athlete' because it has an aerobic capacity that is 2 or 3 times greater than species of similar body size (i.e. steers; Jones et al. 1989). Racing breeds, such as the Thoroughbred and Standardbred, can achieve a relatively high VO 2max of 153 ml O 2 /kg min (Rose et al. 1988) and 140 ml O 2 /kg min (Tyler et al. 1996) respectively. Maximal whole body oxygen uptake ( VO 2max ) is defined as the highest rate at which oxygen can be utilised by the body. It is related to chronic physical activity, body composition and relative health of the individual animal (Pollock and Wilmore 1990).Two important determinants of VO 2max are body size and blood volume. Body size determines the quantity of active tissue while blood volume is important in the regulation and maintenance of cardiac output and the delivery of oxygen to that metabolic tissue and has been shown to be proportional to VO 2max in the comparative literature (Taylor et al. 1982). In man, it has been established that the amount of fat-free mass (FFM) is strongly related to an individual's ability to work at maximal aerobic intensities (Buskirk and Taylor 1957). Furthermore, in man, the relationship between FFM and performance has been well established (Pollock and Wilmore 1990). This relationship has also been observed in the equine athlete, with the most successful pace...

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