Mindy L. Millard-Stafford

Carbohydrate-electrolyte replacement improves distance running performance in the heat

The effects of a 7% carbohydrate-electrolyte drink (CE) and an artificially sweetened placebo (P) on performance and physiological function were compared during a 40-km run in the heat. Eight highly trained male runners completed two runs on a measured outdoor course. The first 35 km of each run was performed at self-selected training pace and the last 5 km at race effort. Under a counterbalanced, double-blind design, subjects consumed 400 ml of either CE or P 30 min prior to exercise, and 250 ml every 5 km thereafter during the run. Rectal temperature, heart rate, rating of perceived exertion, sweat rate, and respiratory exchange ratio were similar during the run for CE and P. Serum Na+, K+, Cl-, total protein, osmolality, blood lactate, urea nitrogen, and % change in plasma volume were also similar for both drink conditions; however, blood glucose was significantly higher (P less than 0.01) with CE. Running performance in the last 5 km was significantly faster (P less than 0.03) during CE (21.9 min) compared with P (24.4 min). Subjects reported no differences in stomach upset, bloating, or nausea between P and CE. Results indicate that CE replacement elicits similar thermoregulatory and physiological responses during prolonged running in the heat but increases run performance and blood glucose when compared with P.

Carbohydrate-electrolyte replacement during a simulated triathlon in the heat

Effects of a 7% carbohydrate-electrolyte drink (CE) or a flavored water placebo (P) on physiological function and performance were compared during a simulated triathlon (ST) in the heat. Ten trained male triathletes performed two STs, consisting of 1.5 km swimming, 40 km cycling, and 10 km running in an environmentally controlled area at self-selected race pace. Subjects consumed 2 ml.kg-1 (130-174 ml) of CE or P following the swim, at 8.0-km intervals during cycling, and at 3.2-km intervals during running. Sweat rate, rectal and mean skin temperatures, perceived exertion, heart rate, plasma osmolality, percent change in plasma volume, total protein, Na+, K+, and lactate were similar during the ST under both drink conditions, but RER and plasma glucose were higher (P less than 0.05) with CE. During the last 4 km of running, VO2 was significantly higher with CE. Mean run time and total ST time were faster with CE (by 1.4 and 1.2 min) although not significantly different (P less than 0.06 and P less than 0.10) from P. Subjects reported no significant difference in nausea, fullness, or stomach upset with CE compared to P. General physiological responses were similar for each drink during 2 h of multi-modal exercise in the heat; however, blood glucose, carbohydrate utilization, and exercise intensity at the end of a ST may be increased with CE fluid replacement.

Running-specific prostheses permit energy cost similar to nonamputees.

UNLABELLED Improvements in prosthesis design have facilitated participation in competitive running for persons with lower limb loss (AMP). PURPOSE The purpose of this study was to examine the physiological responses of AMP using a run-specific prosthesis (RP) versus a traditional prosthesis (P) and cross-referenced with nonamputee controls (C) matched by training status, age, gender, and body composition during level treadmill running (TM). METHODS Twelve trained runners completed a multistage submaximal TM exercise during which HR and oxygen uptake (VO(2)) were obtained. Steady state measures at 134 m x min(-1) were compared between RP and P in AMP. AMP using RP (AMP-RP) and C also performed a continuous speed-incremented maximal TM test until volitional fatigue. RESULTS RP elicited lower HR and VO(2) compared with P in AMP. Using RP, AMP achieved similar VO(2max) and peak TM speed compared with C but with higher HR(max). Relative HR (%HR(max)) and oxygen uptake (%VO(2max)), the regression intercept, slope, SEE, and Pearsons r correlation were not different between AMP-RP and C. %HR(max) calculated with the published equation, %HR(max) = 0.73(%VO(2max)) + 30, was not significantly different from actual %HR(max) for AMP-RP or C in any stage. CONCLUSIONS RP permits AMP to attain peak TM speed and aerobic capacity similar to trained nonamputees and significantly attenuates HR and energy cost of submaximal running compared with a P. Use of RP confers no physiological advantage compared with nonamputee runners because energy cost at the set speed was not significantly different for AMP-RP. Current equations on the basis of the relative HR-VO(2) relationship seem appropriate to prescribe exercise intensity for persons with transtibial amputations using RP.

Impact of bone mineral estimates on percent fat estimates from a four-component model

PURPOSE The primary purpose of this study was to determine the impact of bone mineral content (BMC) from QDR 1000/W and DPX-L dual-energy x-ray absorptiometers (DXA(QDR) and DXA(DPX-L) on percent fat (%fat) estimates from a four-component model. A secondary purpose was to test the accuracy of %fat estimates from DXA(QDR) and DXA(DPX-L) using %fat estimates from a four-component model as the criterion. METHODS Percent fat, fat mass, and fat-free mass (FFM) were determined from DXA(QDR) and DXA(DPX-L) and from a four-component model based on measures of body density from underwater weighing, body water from deuterium dilution, and BMC from DXA(QDR) (4C(QDR)) or DXA(DPX-L) (4C(DPX-L)) in young men (N = 14) and women (N = 10). RESULTS BMC was significantly lower using DXA(QDR) compared with DXA(DPX-L) (approximately 11%), resulting in slightly lower estimates of %fat and fat mass and slightly higher estimates of FFM from 4C(QDR) than 4C(DPX-L). Although estimates of %fat, fat mass, and FFM from DXA(QDR) and DXA(DPX-L) were not different than those from a four-component model, there was considerable individual variability between methods. Furthermore, %fat from DXA(QDR) was lower than %fat from 4C(DPX-L). CONCLUSIONS We conclude that using BMC from different DXA instruments has a minimal impact on %fat, fat mass, and FFM estimates from a four-component model. The large variability in %fat estimates between the two DXA instruments and those from a four-component model does not support DXA as a criterion method of body composition. Further studies involving larger sample sizes and specific population groups are needed to assess the validity of body composition measurements from DXA.

Effect of glucose polymer diet supplement on responses to prolonged successive swimming, cycling and running

SummaryFifteen male endurance athletes were studied to determine the effect of a glucose polymer (GP) diet supplement on physiological and perceptual responses to successive swimming, cycling and running exercise. Thirty min of swimming, cycling and running at 70%

MONITORING CORE TEMPERATURE DURING EXERCISE: INGESTIBLE SENSOR VS RECTAL THERMISTOR

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Caffeinated Sports Drink: Ergogenic Effects and Possible Mechanisms

, followed by a run to exhaustion at 90%