J. A. Houmard

Effects of repeated days of intensified training on muscle glycogen and swimming performance.

Twelve, highly trained male swimmers were studied before, during, and after 10 successive days of increased training in an attempt to determine the physical effects of training over-load. Their average training distance was increased from 4,266 to 8,970 m.d-1, while swimming intensity was maintained at 94% (SE +/- 2%) of their maximal oxygen uptake, resulting in an average caloric cost during training of 2,293 kcal.d-1 (+/- 74). As a result of the intensified training regimen, the swimmers experienced local muscular fatigue and difficulty in completing the training sessions. Nevertheless, their swimming power, sprinting (s.22.86 m-1), endurance (s.365.8 m-1) performance, aerobic capacity, and muscle (m. deltoid) citrate synthase were unchanged as a consequence of the 10-d training regimen. Four of the 12 swimmers were, however, unable to tolerate the heavier training demands, and were forced to swim at significantly slower (P less than 0.05) speeds during the training sessions. These men were found to have significantly reduced muscle glycogen values, which was the result of their abnormally low carbohydrate intake. The findings of this research suggest that some swimmers may experience chronic muscular fatigue as a result of their failure to ingest sufficient carbohydrate to match the energy demands of heavy training.

Physiological responses to successive days of intense training in competitive swimmers

To examine the physiological responses to successive days of intense training, 12 male collegiate swimmers doubled their training distance (4,266 +/- 264 to 8,970 +/- 161 m.d-1) while maintaining the intensity at approximately 95% VO2max for 10 d. Blood samples were obtained pre-exercise and immediately and 5 min after a sub-maximal (approximately 95% VO2max) front crawl swim (365.8 m) on days 0, 5, and 11. Swim performance was assessed from a maximal front crawl swim (365.8 m), two maximal front crawl sprints (22.9 m), and a semi-tethered swim power test. No significant changes were observed in performance. Pre-exercise serum cortisol (17.5 +/- 1.5, 19.5 +/- 1.6, and 20.6 +/- 1.2 micrograms.dl-1 for days 0, 5, and 11, respectively) and creatine kinase (56.2 +/- 7.7, 93.1 +/- 10.1, and 119.0 +/- 23.1 U.l-1 for days 0, 5, and 11, respectively) values were significantly elevated (P less than 0.05) on days 5 and 11 compared to day 0. Resting plasma catecholamine concentrations were higher but not significantly different (P greater than 0.05) at the end of the training period. Measurements of hemoglobin and hematocrit indicated a relative increase of 11.4 +/- 2.7% (P less than 0.05) in estimated plasma volume during the training period. Resting blood glucose values were unaffected by the training regimen while small but significant decreases in resting blood lactate values (1.01 +/- 0.06, 0.85 +/- 0.06, and 0.86 +/- 0.06 mmol.l-1 for days 0, 5, and 11, respectively) were observed on days 5 and 11. Resting heart rate and systolic blood pressure were not affected by the increased training load.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of sodium bicarbonate on sprint performance: Relationship to dosage

The purpose of this investigation was to determine the minimum oral dosage of bicarbonate needed to significantly elevate blood bicarbonate and the influence of induced alkalosis on performance in high-intensity, short-duration exercise. Nine endurance-trained cyclists performed four 2-min sprints on separate occasions using an isokinetic cycle ergometer (Fitron, Cybex, Inc.). One hour before each test, the cyclists consumed either a placebo (A), a solution of 0.10 g NaHCO3.kg-1 body weight (B), a solution of 0.15 g NaHCO3.kg-1 body weight (C), or a solution of 0.20 g NaHCO3.kg-1 body weight (D) in random order. Arterialized venous blood was taken before (PRE) and after (POST) ingestion, and 1, 3, 5, 10, and 15 min following the 2-min bike sprint. The results showed a significant increase in POST blood bicarbonate, and the elevation was incrementally related to the dosage. There was, however, no significant improvement in performance. Total work (mean +/- SE) for each treatment (N.m per 2 min) were: A, 47,267 (+/- 2,472); B, 47,004 (+/- 3,094); C, 46,312 (+/- 2,964); and D, 47,190 (+/- 2,621). The results of this study show that incremental doses of NaHCO3 of 0.20 g.kg-1 and below produce incremental elevations in blood bicarbonate but do not produce improvements in performance for a sprint bout lasting 2 min.

Gastric emptying: influence of prolonged exercise and carbohydrate concentration.

Gastric emptying: influence of prolonged exercise and carbohydrate concentration, Med. Sci. Sports Exerc., Vol. 21, No. 3, pp. 269-274, 1989. The purpose of this study was to examine the effects of serial feedings of different concentrations of carbohydrate (CHO) on gastric emptying and to compare the rates of gastric emptying at rest and during prolonged exercise. Solutions of 0, 6, 12, and 18 g. 100 ml-1 (WP, CHO-6, CHO-12, and CHO-18, respectively) were tested. Ten trained male cyclists performed five trials involving 120 min of cycling. The first 105 min were at 70% of VO2max, and the final 15 min were an all-out self-paced performance ride. In one of the five trials, the subjects rode intermittently, completing seven 15-min rides at 70% of VO2max, with 3 min of rest between each ride. Every 15 min, approximately 150 ml (8.5 ml.kg-1.h-1) of one of the four test solutions were consumed. (In the intermittent trial, the CHO-12 solution was used.) Subjects were also tested during 120 min of seated rest using the above feeding schedule (6% solution). Gastric residue was determined by stomach aspiration following the performance ride. The volumes emptied during the CHO-12 and CHO-18 trials (1,049.8 and 889.2 ml) were significantly different from each other and were less than during the WP and CHO-6 trials (1,210.3 and 1,185.6 ml) (P less than 0.05). CHO delivery was significantly higher in the CHO-12 and CHO-18 trials (126 and 160 g) compared to the CHO-6 trial (71.1 g).(ABSTRACT TRUNCATED AT 250 WORDS)

The role of anaerobic ability in middle distance running performance

SummaryThe purpose of this study was to assess the relationship between anaerobic ability and middle distance running performance. Ten runners of similar performance capacities (5 km times: 16.72, SE 0.2 min) were examined during 4 weeks of controlled training. The runners performed a battery of tests each week [maximum oxygen consumption (VO2max), vertical jump, and Margaria power run] and raced 5 km three times (weeks 1, 2, 4) on an indoor 200-m track (all subjects competing). Regression analysis revealed that the combination of time to exhaustion (TTE) during theVO2max test (r2=0.63) and measures from the Margaria power test (W·kg−1,r2=0.18 ; W,r2=0.05) accounted for 86% of the total variance in race times (P<0.05). Regression analysis demonstrated that TTE was influenced by both anaerobic ability [vertical jump, power (W·kg−1) and aerobic capacity (VO2max, ml·kg−1·min−1)]. These results indicate that the anaerobic systems influence middle distance performance in runners of similar abilities.