To study the physiologic basis of variability of physical performance in the laboratory, ten male subjects were studied once a week, during a 9-12 month period. Previously, the reference maximal work load attained (Wref) was determined in each subject. The test protocol of the actual study was based on the individual Wref and started at 70% Wref for 5 min whereupon the work load was increased by 5% Wref every 2.5 min to exhaustion. The maximal work load attained (Wmax) was considered as the test performance. Heart rate, respiratory variables, oxygen uptake (VO2), and blood lactate concentration were determined at each work load. The rate of perceived exertion during submaximal and maximal work was also scored. In all subjects, Wmax and VO2max varied randomly, while the coefficient of variation in VO2max (4.20% - 11.35%) exceeded that in Wmax (2.95%-6.83%). No seasonal influences on VO2 max and Wmax were observed. In all subjects the physiologic variables, when plotted as a function of external work load, were shifted to the right with higher Wmax values and to the left with lower Wmax values. With lower Wmax values, the rate of perceived exertion during submaximal work tended to increase. The results suggest that the magnitude of physiologic responses to exercise is related to relative work load and that variability of physical performance is related to changes in gross mechanical efficiency.

Physical activity has a beneficial effect on insulin sensitivity in normal as well as insulin resistant populations. A distinction should be made between the acute effects of exercise and genuine training effects. Up to two hours after exercise, glucose uptake is in part elevated due to insulin independent mechanisms, probably involving a contraction-induced increase in the amount of GLUT4 associated with the plasma membrane and T-tubules. However, a single bout of exercise can increase insulin sensitivity for at least 16 h post exercise in healthy as well as NIDDM subjects. Recent studies have accordingly shown that acute exercise also enhances insulin stimulated GLUT4 translocation. Increases in muscle GLUT4 protein content contribute to this effect, and in addition it has been hypothesized that the depletion of muscle glycogen stores with exercise plays a role herein. Physical training potentiates the effect of exercise on insulin sensitivity through multiple adaptations in glucose transport and metabolism. In addition, training may elicit favourable changes in lipid metabolism and can bring about improvements in the regulation of hepatic glucose output, which is especially relevant to NIDDM. It is concluded that physical training can be considered to play an important, if not essential role in the treatment and prevention of insulin insensitivity.

In order to determine the ventilatory threshold (VT) and the lactate threshold (LT) in a reliable way, a new method is proposed and compared with conventional methods. The new method consists of calculating the point that yields the maximal distance from a curve representing ventilatory and metabolic variables as a function of oxygen uptake (VO2) to the line formed by the two end points of the curve (Dmax method). Male cyclists (n = 8) performed two incremental exercise tests a week apart. Ventilatory/metabolic variables were measured and blood was sampled for later lactate measurement during each workload and immediately after exercise. No statistical differences were observed in the threshold values (expressed as absolute oxygen uptake; VO2) determined by the Dmax method and the conventional linear regression method (according to O2 equivalent; EqO2) and venous blood at the onset of blood lactate (OBLA), while VT assessed with the conventional linear method (according to the slope of CO2 output; Vslope) yielded significantly lower threshold values. Similar results were obtained from the reproducibility test. Thus, the Dmax method appears to be an objective and reliable method for threshold determination, which can be applied to various ventilatory or metabolic variables yet yield similar results. The results also showed that breathing frequency can be used to determine VT.

The present study was designed to determine postexercise muscle protein synthesis and whole body protein balance following the combined ingestion of carbohydrate with or without protein and/or free leucine. Eight male subjects were randomly assigned to three trials in which they consumed drinks containing either carbohydrate (CHO), carbohydrate and protein (CHO+PRO), or carbohydrate, protein, and free leucine (CHO+PRO+Leu) following 45 min of resistance exercise. A primed, continuous infusion of L-[ring-13C6]phenylalanine was applied, with blood samples and muscle biopsies collected to assess fractional synthetic rate (FSR) in the vastus lateralis muscle as well as whole body protein turnover during 6 h of postexercise recovery. Plasma insulin response was higher in the CHO+PRO+Leu compared with the CHO and CHO+PRO trials (+240 +/- 19% and +77 +/- 11%, respectively, P < 0.05). Whole body protein breakdown rates were lower, and whole body protein synthesis rates were higher, in the CHO+PRO and CHO+PRO+Leu trials compared with the CHO trial (P < 0.05). Addition of leucine in the CHO+PRO+Leu trial resulted in a lower protein oxidation rate compared with the CHO+PRO trial. Protein balance was negative during recovery in the CHO trial but positive in the CHO+PRO and CHO+PRO+Leu trials. In the CHO+PRO+Leu trial, whole body net protein balance was significantly greater compared with values observed in the CHO+PRO and CHO trials (P < 0.05). Mixed muscle FSR, measured over a 6-h period of postexercise recovery, was significantly greater in the CHO+PRO+Leu trial compared with the CHO trial (0.095 +/- 0.006 vs. 0.061 +/- 0.008%/h, respectively, P < 0.05), with intermediate values observed in the CHO+PRO trial (0.0820 +/- 0.0104%/h). We conclude that coingestion of protein and leucine stimulates muscle protein synthesis and optimizes whole body protein balance compared with the intake of carbohydrate only.

Fat and carbohydrate are the principal substrates that fuel aerobic ATP synthesis in skeletal muscle. Endogenous carbohydrates, mainly stored as muscle and liver glycogen, represent less than 5 % of total energy storage in an average man. The vast majority of our energy reserves is stored as fat, mainly deposited as triacylglycerol (TG) in subcutaneous and deep visceral adipose tissue. Smaller quantities of TG are present in circulating lipoprotein particles and in lipid droplets inside the muscle fibres, intramyocellular triacylglycerol (IMTG;Hoppeler et al. 1985). The latter has recently regained much attention due to the proposed functional relationship between IMTG accumulation and the development of insulin resistance (Boden et al. 2001). It is speculated that elevated free fatty acid (FFA) delivery and/or impaired FA oxidation result in intramyocellular accumulation of TG and FA metabolites, which could induce defects in the insulin signalling cascade, causing skeletal muscle insulin resistance. The progressive accumulation of IMTG in sedentary, obese and/or type 2 diabetes patients should therefore form a major therapeutic target and efforts should be made to develop interventions that prevent excess IMTG accretion by stimulating their rate of oxidation. However, the latter is complicated by the fact that information on the regulation of IMTG metabolism is scarce.Several studies applying FA isotope tracers have shown that during moderate intensity exercise ~40-60 % of total fat oxidation is accounted for by plasma derived FFA oxidation in endurance trained male subjects following an overnight fast (Romijn et al. 1993;Sidossis et al. 1998;Coyle et al. 2001;van Loon et al. 2001). This implies that other fat sources can contribute substantially to total fat oxidation during exercise. However, the relative contribution of these other fat sources to energy expenditure has been shown to depend on exercise Both stable isotope methodology and fluorescence microscopy were applied to define the use of intramuscular triglyceride (IMTG) stores as a substrate source during exercise on a whole-body as well as on a fibre type-specific intramyocellular level in trained male cyclists. Following an overnight fast, eight subjects were studied at rest, during 120 min of moderate intensity exercise (60 % maximal oxygen uptake capacity (◊J ,max )) and 120 min of post-exercise recovery. Continuous infusions of [U-13 C]palmitate and [6,6-2 H 2 ]glucose were administered at rest and during subsequent exercise to quantify whole-body plasma free fatty acid (FFA) and glucose oxidation rates and the contribution of other fat sources (sum of muscle-plus lipoprotein-derived TG) and muscle glycogen to total energy expenditure. Fibre type-specific intramyocellular lipid content was determined in muscle biopsy samples collected before, immediately after and 2 h after exercise. At rest, fat oxidation provided 66 ± 5 % of total energy expenditure, with FFA and other fat sources contributing 48 ± 6 and 17 ± 3 %, respectively. FFA oxidation r...