Decrements in muscle function may reduce physical and skilled performance and have been shown to be greater following walking unloaded on negative gradients. We examined the effects of prolonged ...walking with load carriage at level and negative gradients on muscle function.
There were 10 male participants who completed two bouts of load carriage carrying a 25-kg backpack for 2 h at 6.5 km x h(-1) during level walking (LW) and downhill (-8% gradient) walking (DW). Force produced during voluntary and electrically stimulated contractions was measured before, 0, 24, 48, and 72 h post-exercise.
Isometric knee extension force decreased immediately after LW (15 +/- 11%) and DW (16 +/- 17%) and recovered to baseline at 72 h. Voluntary activation decreased immediately after LW (95 +/- 5 to 91 +/- 10%) and DW (97 +/- 4 to 94 +/- 12%) and returned to baseline at 24 h. Electrically stimulated 20:50 Hz tetani decreased after LW and DW, with complete recovery by 24 h after DW only. LW and DW caused decreases immediately after exercise in isokinetic peak torque of knee extensors and flexors at 60 degrees x s(-1) and 180 degrees x s(-1), trunk extensors and flexors at 15 degrees x s(-1), and shoulder flexors at 60 degrees x s(-1), with complete recovery at different time points, but all by 72 h.
Level and downhill treadmill walking with load carriage resulted in similar changes in muscle function of the lower and upper body muscles immediately after exercise and during recovery. The decrements in muscle function may increase the risk of musculoskeletal injury and is likely to impair performance during physical and skilled tasks following load carriage.
The aim of this study was to determine the incidence of subject drop-out on a multi-stage shuttle run test and a modified incremental shuttle run test in which speed was increased by 0.014m.s-1 every ...20-m shuttle to avoid the need for verbal speed cues. Analysis of the multi-stage shuttle run test with 208 elite female netball players and 381 elite male lacrosse players found that 13 (+/-3) players stopped after the first shuttle of each new level, in comparison with 5 (+/-2) players on any other shuttle. No obvious drop-out pattern was observed on the incremental shuttle run test with 273 male and 79 female undergraduate students. The mean difference between a test-retest condition (n= 20) for peak shuttle running speed (-0.03+/- 0.01m.s-1) and maximal heart rate (0.4+/- 0.1 beats.min-1) on the incremental test showed no bias (P > 0.05). The 95% absolute confidence limits of agreement were 0.11m.s-1 for peak shuttle running speed and +/-5 beats.min-1 for maximal heart rate. The relationship (n= 27) between peak shuttle running speed on the incremental shuttle run test (4.22+/- 0.14m.s-1) and VO2max (59.0+/- 1.7ml.kg-1.min-1) was r=0.91 (P< 0.01), with a standard error of prediction of 2.6ml.kg-1.min-1. These results suggest verbal cues during the multi-stage shuttle run test may influence subject drop-out. The incremental shuttle run test shows no obvious drop-out patten and provides a valid estimate of VO2max.
This study examined the influence of water ingestion on endurance capacity during submaximal treadmill running. Four men and four women with a mean (± S.E.) age of 21.4 ± 0.7 years, height of 169 + 2 ...cm, body mass of 63.1 ± 2.9 kg and VO
2
max of 51.1 ± 1.8 ml kg
−1
min
−1
, performed two randomly assigned treadmill runs at 70% VO
2
max to exhaustion. No fluid was ingested during one trial (NF-trial), whereas a single water bolus of 3.0 ml kg
−1
body mass was ingested immediately pre-exercise and serial feedings of 2.0 ml kg
−1
body mass were ingested every 15 min during exercise in a fluid replacement trial (FR-trial). Run time for the NF-trial was 77.7 ± 7.7 min, compared to 103 ± 12.4 min for the FR-trial (P<0.01). Body mass (corrected for water ingestion) decreased by 2.0 ± 0.2% in the NF-trial and 2.7 ± 0.2% in the FR-trial (P<0.01), while plasma volume decreased by 1.1 ± 1.1% and 3.5 ± 1.1% in the two trials respectively (N.S.). However, these apparent differences in circulatory volume were not associated with differences in rectal temperature. Respiratory exchange ratios indicated increased carbohydrate metabolism (73% vs 64% of total energy expenditure) and suppressed fat metabolism after 75 min of exercise in the NF-trial compared with the FR-trial (NF-trial, 0.90 ± 0.01; FR-trial, 0.86 ± 0.03; P<0.01). Blood glucose concentrations were similar in both trials, while blood lactate concentrations were higher in the NF-trial at the end of exercise (4.83 ± 0.34 vs 4.18 ± 0.38 mM; P<0.05). In summary, water ingestion during prolonged running improved endurance capacity.
Recovery from prolonged exercise involves both rehydration and replenishment of endogenous carbohydrate stores. The present study examined the influence of ingesting a carbohydrate-electrolyte (CE) ...solution following prolonged running, on exercise capacity 4 hr later. Twelve men and 4 women were divided into two matched groups, which were randomly assigned to either a control (P) or a carbohydrate (CHO) condition. Both groups ran at 70% of maximal oxygen uptake (VO2max) on a level treadmill for 90 min or until volitional fatigue (R1), and they ran at the same %VO2max to exhaustion 4 hr later to assess endurance capacity (R2). The CHO group ingested a 6.9% CE solution providing 1.0 g CHO.kg body weight-1 immediately post-R1 and again 2 hr later. The P group ingested equal volumes of a placebo solution. Run times (mean +/- SEM) for R1 did not differ between the groups (P 86.3 +/- 3.8 min; CHO 87.5 +/- 2.5 min). The CHO group ran 22.2 (+/-3.5) min longer than the P group during R2 (P 39.8 +/- 6.1 min; CHO 62.0 +/- 6.2 min) (p 0.05). Thus, ingesting a 6.9% carbohydrate-electrolyte beverage following prolonged, constant-pace running improves endurance capacity 4 hr later
Whilst the metabolic responses to submaximal exercise are relatively well documented, little information is available relating to recovery and further exercise performance. Thus, the principal aim of ...this research was to investigate the influence of nutrition on recovery from prolonged, constant pace running. In the first study (Chapter 4), the influence of increased carbohydrate intake on endurance capacity was investigated following a bout of prolonged, constant pace running and a 22.5-h recovery. Sixteen male subjects were divided into two matched groups, which were randomly assigned to either a control (CON) or a carbohydrate (CHO) condition. Both groups ran at 70% .VO2max on a level treadmill for 90 min, or until volitional fatigue, whichever came first (R1). Subjects ran at the same % .VO2max for as long as possible 22.5-h later, as an assessment of endurance capacity (R2). During the recovery, the carbohydrate intake of the CHO group was increased from 5.8 ( 0.5) to 8.8 ( 0.1) g-kg-1 body wt (mean SE). An isocaloric diet was prescribed for the CON group, providing additional energy in the form of dietary fat and protein. Run times for R_1 did not differ between the groups. However, R_2 run time of the CON group was reduced by 15.6 min (p&60 0.05), whilst the CHO group matched their R_1 performance (CON - 70.7 ( 7.2) min; CHO - 91.9 ( 9.0) min). Thus, a high carbohydrate diet restored endurance capacity within 22.5-h, whereas an isocaloric diet without additional carbohydrate did not result in the same restoration of exercise capacity. Exercise-induced dehydration impinges upon both exercise capacity and the capacity of the body to recover. The second study (Chapter 5), investigated the influence of water ingestion on endurance capacity during constant pace running. Four men and four women completed two randomly assigned treadmill runs at 70% .VO_2max to volitional fatigue. During one trial, no fluid was ingested during exercise (NF). Whereas, during the fluid replacement (FR) trial a single water bolus equivalent to 3.0 ml.kg-1 body wt was provided pre-exercise, followed by serial feedings equivalent to 2.0 ml.kg-1 body wt 15 min-1 during exercise. Run time during the NF-trial was 77.7 ( 7.7) min, compared to 103.0 ( 12.4) min during the FR-trial (p< 0.01)
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