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|Title:||Protein Turnover in Trained Male and Female Endurance Athletes|
|Abstract:||The dietary protein requirements of endurance trained athletes have been previously shown to be higher or no different than those of sedentary persons. However, the current Canadian Recommended Nutrient Intake (RNI) for protein contains no allowance for the effects of habitual physical activity. The discrepancy as to whether the protein requirements of active individuals are elevated, is probably due to: varying study designs, the different training status of the subjects, dissimilar exercise intensities, and the dietary condition of the subjects studied. In addition, previous work (Tarnopolsky, LJ et al. J. Appl. Physiol. 68(1):302-308, 1990), has shown that males may catabolize an increased amount of protein, as a result of endurance exercise, compared to females. The present study examined protein turnover in trained male (n=6) and female (n=6) endurance athletes (runners) • Athletes were selected for equal training status and conditioning and were placed on a diet, isoenergetic with their habitual intake, containing protein at the Canadian RNI. All female athletes were tested during the mid-follicular phase of their menstrual cycle. After being adapted to the diet for 10 days during which the athletes exercised according to their habitual exercise schedule, each athlete completed a three day measurement of nitrogen balance. Nitrogen balance showed that the RNI was inadequate for the female athletes (mean± SE), nitrogen balance= -0.89 ± 0.33 g N·d⁻¹ (-15.9 ± 6.0 mg N·kg⁻¹·d⁻¹), and for male athletes, nitrogen balance = -1.69 ± 0.64 g N·d⁻¹ (-26.3 ± 11.0 mg N·kg1·d⁻¹). To examine the kinetics of leucine metabolism during exercise, each subject received a primed constant intravenous infusion of L-[1-¹³C]leucine while resting for 2.0 hand then during a 90 minute treadmill run at approximately 65% of VO₂ₘₐₓ. Blood samples were taken at steady state and analyzed for ¹³CO enrichment of a-ketoisocaproic acid and expired gas samples were analyzed for ¹³CO₂ enrichment. Corrections were made for changes in background ¹³CO₂/ ¹²CO₂ and changes in bicarbonate retention factor, during exercise, were also determined. Measurements of whole-body leucine kinetics (flux, oxidation, and non-oxidative leucine disposal) were calculated using the reciprocal pool model. Exercise resulted in a significant increase (P<O. 001) in leucine oxidation in both males and females. The increase was 95% above resting in females and 84% above resting in males. Male athletes oxidized a greater amount of leucine during the infusion than female athletes (P=O. 004). Leucine flux increased significantly (P<O. 001) during exercise in both groups of athletes. The non-oxidative portion of leucine flux did not change significantly throughout the infusion in either male or female subjects. Oxidation of leucine could account for 88% of the negative nitrogen balance in the female athletes and 90% of the negative nitrogen balance in the male athletes. It is concluded that the Canadian RNI for protein is inadequate for those persons who continually engage in endurance activities. In addition, leucine oxidation during prolonged sub-maximal exercise is greater in males than females and the increase in amino acid oxidation could account for approximately 90% of the negative nitrogen balance observed in these groups of athletes. Future investigations of protein requirements for athletes should consider males and females as distinct groups.|
|Appears in Collections:||Digitized Open Access Dissertations and Theses|
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