Effects of medium-chain triglyceride ingestion on fuel metabolism and cycling performance.

On three occasions separated by 10 days, six endurance-trained cyclists rode for 2 h at 60% of peak O2 uptake and then performed a simulated 40-km time trial (T-trial). During the rides, the subjects ingested a total of 2 liters of a [U-14C]glucose-labeled beverage containing a random order of either 10% glucose [carbohydrate (CHO)], 4.3% medium-chain triglycerides (MCTs); or 10% glucose + 4.3% MCTs (CHO+MCT). Although replacing CHO with MCTs slowed the T-trials from 66.8 +/- 0.4 (SE) to 72.1 +/- 0.6 min (P < 0.001), adding MCTs to CHO improved the T-trials from 66.8 +/- 0.4 to 65.1 +/- 0.5 min (P < 0.05). Faster T-trials in the CHO+MCT trial than in the CHO trial were associated with increased final circulating concentrations of free fatty acids (0.58 +/- 0.09 vs. 0.36 +/- 0.06 mmol/l; P < 0.05) and ketones (1.51 +/- 0.25 vs. 0.51 +/- 0.07 mmol/l; P < 0.01) and decreased final circulating concentrations of glucose (5.2 +/- 0.2 vs. 6.3 +/- 0.3 mmol/l; P < 0.01) and lactate (1.9 +/- 0.4 vs. 3.7 +/- 0.5 mmol/l; P < 0.05). Adding MCTs to ingested CHO reduced total CHO oxidation rates from 14 +/- 1 to 10 +/- 1 mmol/min at 2 h and from 17 +/- 1 to 14 +/- 1 mmol/min in the T-trial (P < 0.01), without affecting the corresponding approximately 5 and approximately 7 mmol/min rates of [14C]glucose oxidation. These data suggest that MCT oxidation decreased the direct and/or indirect (via lactate) oxidation of muscle glycogen. A reduced reliance on CHO oxidation at a given O2 uptake is similar to an endurance-training effect, and that may explain the improved T-trial performances.

Anabolic-androgenic steroid increases running endurance in rats.

The study was designed to determine whether treatment with an anabolic-androgenic steroid enhances running performance in rats by increasing their freely chosen training distance. Forty male Long-Evans rats were randomly divided into either a sedentary control group or an exercising group caged in specially designed running wheels in which the rats were able to run spontaneously. After 4 wk, both groups were further subdivided into two groups receiving either 0.5-mg Durabolin (nandrolone phenylpropionate) (im) or 0.5-mg saline, every second day. After 8 wk, running distance was similar in both exercising groups. Rats receiving the anabolic-androgenic steroid ran 41% longer during the test of submaximal running endurance compared to the trained rats receiving saline (P < 0.05). Submaximal running endurance was not increased in sedentary rats receiving the anabolic-androgenic steroid. After 4 wk of training, the maximal sprinting speed increased by 29% in trained rats. There was no further increase in maximal sprinting speed after an additional 4 wk of training and treatment with either anabolic-androgenic steroid or saline treatment. Therefore, rats that train spontaneously while being treated with an anabolic-androgenic steroid had increased submaximal running endurance compared with trained rats treated with saline, despite the similar voluntary training distance and skeletal muscle oxidative capacity between the two groups. The mechanism by which treatment with an anabolic-androgenic steroid, combined with training, enhances submaximal running performance could not be identified and needs to be addressed in future studies.

Running intensity as determined by heart rate is the same in fast and slow runners in both the 10- and 21-km races.

The aims of this study were to determine (1) whether running speed is directly proportional to heart rate (HR) during field testing and during 10- and 21-km races, and (2) whether running intensity, as estimated from HR measurements, differs in 10- and 21-km races and between slow and fast runners at those running distances. Male runners were divided into a fast (65-80 min for 21 km; n = 8) or slow (85-110 min for 21 km; n = 8) group. They then competed in 10- and 21-km races while wearing HR monitors. All subjects also ran in a field test in which HR was measured while they ran at predetermined speeds. The 10-km time was significantly less in the fast compared with the slow group (33:15 +/- 1:42 vs 40:07 +/- 3:01 min:s; mean +/- S.D.), as was 21-km time (74:19 +/- 4:30 vs 94:13 +/- 9:54 min:s) (P < 0.01). Despite the differences in running speed, the average running intensity (%HRmax) for the fast and slow groups in the 10-km race was 90 +/- 1 vs 89 +/- 3% and in the 21-km race 91 +/- 1 vs 89 +/- 2%, respectively. In addition, %HRmax was consistently lower in the field test at the comparative average running speeds sustained in the 10-km (P < 0.01) and 21-km (P < 0.001) races. Hence, factors in addition to work rate or running speed influence the HR response during competitive racing. This finding must be considered when running intensity for competitive events is prescribed on the basis of field testing performed under non-competitive conditions in fast and slow runners.