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PubMed1982

The effect of stride length variation on oxygen uptake during distance running.

Ten recreational runners (mean VO2max 64.7 ml . kg-1 . min-1) underwent a 5-d acclimation period to treadmill running at a 7 min . mile-1 pace (3.83 m . s-1) for 30 min each day. During these runs their freely chosen stride lengths were determined and expressed as a percentage of leg length (%LL). On two subsequent testing days stride length was systematically varied over a range of +/- 20% LL about the freely chosen value. O2 uptake was determined by the Douglas Bag method. All subjects exhibited a stride length of which O2 uptake was minimized, although the individual profiles varied considerably. The mean increases in VO2 were 2.6 and 3.4 ml . kg-1 . min-1 at the short- and long-stride length extremes, respectively. During unrestricted running deviations from optimal stride length caused a mean increase in VO2 of 0.2 ml . kg-1 . min-1. The relatively efficient running patterns used by the subjects during unrestricted running indicate either an adaption to the chosen stride length through training or a successful process of energy optimization.

Adaptation, Physiological↗

PubMed1995

Maximal and ventilatory threshold responses to treadmill and water immersion running.

This study compared the metabolic responses of 13 endurance runners, familiar with nonweight-bearing water immersion (WI) running, at ventilatory threshold (Tvent) and maximal effort (VO2max) for both treadmill and WI running performance. Oxygen consumption (VO2), ventilation (VE), heart-rate (HR), VE/VO2, respiratory exchange ratio (RER), perceived exertion (RPE), and stride frequency (SF) were measured at Tvent and VO2max. Paired t-tests revealed higher VO2max (59.7 vs 54.6 ml.kg.-1min-1), HRmax (190 vs 175 bpm), RERmax (1.20 vs 1.10), VO2 at Tvent (46.3 vs 42.8 ml.kg.-1min-1), HR at Tvent (165 vs 152 bpm) for treadmill versus WI running, respectively. Treadmill and WI VEmax (109.0 vs 105.8 l.min-1), RPEmax (20), VE at Tvent (66.4 vs 65.7 l.min-1), RER at Tvent (0.99 vs 0.98), RPE at Tvent (13 vs 12) were similar, as were blood lactate [BLa] values obtained at 30 s (10.4 vs 9.8 mmol.l-1) and 5 min (9.7 vs 9.2 mmol.l-1) post-test. SF values over time were higher on the treadmill. The lower WI VO2max with similar peak [BLa] and lower SF values suggests that the active musculature and muscle recruitment patterns differ in WI running due to the high viscosity friction of water, and the nonweight-bearing nature of WI running.

Adult↗

PubMed2003

Physiological correlates with endurance running performance in trained adolescents.

PURPOSE: To examine the relationship between competitive 800-m and 1500-m performance times and a number of physiological variables in a group of endurance-trained, adolescent runners. METHODS: Twenty-three boys and 17 girls volunteered to participate in the study. Track-based, running performance times were available for 18 boys and 14 girls for the 800 m, and 16 boys and 13 girls for the 1500 m. The relationships between these times and the following physiological variables were determined: peak VO(2) running economy (RE), estimated running speed at peak vV0(2peak), peak and mean anaerobic power, and fixed [BLa ] at 2.0, 2.5, and 4.0 mmol.L. RESULTS: RE and vV0(2peak) were significant independent variables for the boys' 800 m (r = 0.62 and -0.62, < 0.01). For the girls, once chronological age was partialled out, none of the measured variables were significantly related to 800-m performance. For the 1500-m event, peak V0(2), vV0(2peak), and the running speed at 2.5 mmol.L (v2.5) were significant independent variables in the boys (r = -0.43, -0.39, and -0.53, < 0.05) and girls (r = -0.50, -0.61, and -0.54, < 0.05). In addition, the V0(2) at 2.5 mmol.L V0(2) (2.5) was related to the 1500-m time in the girls (r = -0.54, < 0.05). CONCLUSION: The physiological variables that were most strongly correlated with middle-distance running performance were v2.5 and the vV0(2peak). To a lesser extent peak V02 may also play a role although it is understood that its contribution may be accounted by vV0(2 peak).

Adolescent↗

PubMed2004

Effects of ingestion of bicarbonate, citrate, lactate, and chloride on sprint running.

PURPOSE: Ingestion of sodium bicarbonate is known to enhance sprint performance, probably via increased buffering of intracellular acidity. The goal was to compare the effect of ingestion of sodium bicarbonate with that of other potential buffering agents (sodium citrate and sodium lactate) and of a placebo (sodium chloride) on sprinting. METHODS: In a double-blind randomized crossover trial, 15 competitive male endurance runners performed a run to exhaustion 90 min after ingestion of each of the agents in the same osmolar dose relative to body mass (3.6 mosmol x kg) on separate days. The agents were packed in gelatin capsules and ingested with 750 mL of water over 90 min. During each treatment we assayed serial finger-prick blood samples for lactate and bicarbonate. A familiarization trial was used to set a treadmill speed for each runner's set of runs. We converted changes in run time between treatments into changes in a time trial of similar duration using the critical-power model, and we estimated likelihood of practical benefit using 0.5% as the smallest worthwhile change in time-trial performance. RESULTS: The mean run times to exhaustion for each treatment were: bicarbonate 82.3 s, lactate 80.2 s, citrate 78.2 s, and chloride 77.4 s. Relative to bicarbonate, the effects on equivalent time-trial time were lactate 1.0%, citrate 2.2%, and chloride 2.7% (90% likely limits +/- 2.1%). Ingested lactate and citrate both appeared to be converted to bicarbonate before the run. There were no substantial differences in gut discomfort between the buffer treatments. CONCLUSION: Bicarbonate is possibly more beneficial to sprint performance than lactate and probably more beneficial than citrate or chloride. We recommend ingestion of sodium bicarbonate to enhance sprint performance.

Adult↗

PubMed2005

The effect of training on running economy and performance in recreational athletes.

PURPOSE: To analyze the effect of an 8-wk training program on the energy cost of running (C) and the performance of 16 recreational males. METHODS: A training group (TG, N = 8, 25.3 +/- 2.9 yr, 183.6 +/- 7.3 cm, 80.9 +/- 9.6 kg) and a control group (CG, N = 8, 24.3 +/- 3.7 yr, 179.3 +/- 6.1 cm, 75.5 +/- 8.0 kg) performed three two-stage tests (TST) at weeks 0, 4, and 8 (W0, W4, W8). Speeds of the first (v-slow) and second stage (v-fast) were 2.4 +/- 0.3 vs 2.5 +/- 0.4 m x s(-1) and 3.7 +/- 0.3 vs 3.9 +/- 0.4 m.s (TG vs CG), respectively. Maximum running time at v-fast (T) served as the measure of performance. C was calculated from oxygen uptake above rest, blood lactate concentration, and speed. The TG trained 3-5x wk(-1) at an HR of +/-10 beats of the HR measured at v-slow at W0 (161 +/- 12 bpm). The CG did not train. RESULTS: At W0, there were no significant differences between the groups in T (377 +/- 47 vs 335 +/- 34 s) and C (v-slow: 4.1 +/- 0.3 vs 4.3 +/- 0.4 J x kg(-1) x m(-1); v-fast: 4.2 +/- 0.4 vs 4.0 +/- 0.4 J x kg(-1) x m(-1)). In the CG, T and C remained almost unchanged at W4 (363 +/- 38 s, 4.0 +/- 0.4 J x kg(-1) x m(-1)) and at W8 (342 +/- 49 s, 4.0 +/- 0.3 J x kg(-1) x m(-1)). In the TG, T increased (P < 0.05) at W4 (469 +/- 45 s) and at W8 (591 +/- 109 s). At v-fast, also C increased (P < 0.05) at W8 (4.6 +/- 0.4 J x kg(-1) x m(-1)), whereas at v-slow, C decreased (P < 0.05) at W4 (3.7 +/- 0.4 J x kg(-1) x m(-1)) with no further change at W8 (3.7 +/- 0.4 J x kg(-1) x m(-1)). CONCLUSION: The training successfully increased running performance in terms of T. During the initial training period, C could be reduced at the speed predominantly used in training. However, at high running speeds, C may even increase if the corresponding running time is largely increased.

Adaptation, Physiological↗

PubMed2005

Are there limits to running world records?

PURPOSE: Previous researchers have adopted linear models to predict athletic running world records, based on records recorded throughout the 20th century. These linear models imply that there is no limit to human performance and that, based on projected estimates, women will eventually run faster than men. The purpose of this article is to assess whether a more biologically sound, flattened "S-shaped" curve could provide a better and more interpretable fit to the data, suggesting that running world records could reach their asymptotic limits some time in the future. METHODS: Middle- and long-distance running world record speeds recorded during the 20th century were modeled using a flattened S-shaped logistic curve. RESULTS: The logistic curves produce significantly better fits to these world records than linear models (assessed by separating/partitioning the explained variance from the logistic and linear models using ANOVA). The models identify a slow rise in world-record speeds during the early year of the century, followed by a period of "acceleration" in the middle of the century (due to the professionalization of sport and advances in technology and science), and a subsequent reduction in the prevalence of record-breaking performances towards the end of the century. The model predicts that men's world records are nearing their asymptotic limits (within 1-3%). Indeed, the current women's 1500-m world record speed of 6.51 m x s(-1) may well have reached its limit (time 3:50.46). CONCLUSIONS: Many of the established men's and women's endurance running world records are nearing their limits and, consequently, women's world records are unlikely to ever reach those achieved by men.

Competitive Behavior↗

PubMed2004

The effect of short-term Swiss ball training on core stability and running economy.

The purpose of this study was to investigate the effect of a short-term Swiss ball training on core stability and running economy. Eighteen young male athletes (15.5 +/- 1.4 years; 62.5 +/- 4.7 kg; sigma9 skinfolds 78.9 +/- 28.2 mm; VO2max 55.3 +/- 5.7 ml.kg(-1).min(-1)) were divided into a control (n = 10) and experimental (n = 8) groups. Athletes were assessed before and after the training program for stature, body mass, core stability, electromyographic activity of the abdominal and back muscles, treadmill VO2max, running economy, and running posture. The experimental group performed 2 Swiss ball training sessions per week for 6 weeks. Data analysis revealed a significant effect of Swiss ball training on core stability in the experimental group (p < 0.05). No significant differences were observed for myoelectric activity of the abdominal and back muscles, treadmill VO2max, running economy, or running posture in either group. It appears Swiss ball training may positively affect core stability without concomitant improvements in physical performance in young athletes. Specificity of exercise selection should be considered.

Abdominal Muscles↗

PubMed2005

Equipment and running surface alter sprint performance of college football players.

The purpose of this study was to determine the effect of football equipment and running surface on sprint performance in NCAA Division II football players (n = 68). Players were timed in the 40-yd sprint on an indoor rubberized track (Day 1) and on an outdoor, natural-grass football field (Day 2) wearing either regulation football equipment or shorts and a T-shirt. Each player was assigned randomly to perform 2 trials under each condition on each surface, and the average of the 2 trials was used for analysis. Offensive backs, defensive backs, and linebackers were significantly faster than were offensive and defensive linemen in all trials, and subjects were collapsed into 2 groups, backs and linemen. Football equipment significantly impaired performance on the track (-2.8% +/- 1.7%) and the field (-2.9% +/- 1.8%). The increase in body mass due to the football equipment was significantly greater for backs (7.2% +/- 0.7%) than for linemen (6.5% +/- 1.0%), but produced a significantly greater impairment in sprint performance in linemen (-3.3% +/- 1.1%) as compared with backs (-2.5% +/- 1.5%). Sprint performance was significantly and equivalently impaired when running on grass (backs: -2.5 +/- 1.1%; linemen: -2.8 +/- 1.4%) as compared with the track. Thus, running a 40-yd sprint in football equipment on a natural grass field impairs performance by an average of 5.5% (+/- 2.3%) compared with running indoors with minimal apparel. Football equipment and running surface significantly impair sprint performance in college football players, the effect being greater in linemen than in backs, and is likely related to differences in muscle strength/power and body fat.

Adult↗

PubMed2005

Proposed tests for measuring the running velocity at the oxygen consumption and heart rate thresholds for treadmill exercise.

The purposes of this study were to (a) determine if the mathematical model used to estimate the physical working capacity at the oxygen consumption threshold (PWC(VO(2))) and physical working capacity at the heart rate threshold (PWC(HRT)) for cycle ergometry could be applied to treadmill running; (b) propose new fatigue thresholds called the running velocity at the oxygen uptake threshold (RV(VO(2))) and running velocity at the heart rate threshold (RV(HRT)) for treadmill exercise; and (c) statistically compare the velocities at the RV(VO(2)), RV(HRT), and ventilatory threshold (VT). Seven aerobically trained adult volunteers (mean +/- SD: age 24.0 +/- 3.9 years, Vo(2) max 56.7 +/- 7.1 ml.kg(-1).min(-1)) performed a maximal treadmill test to determine Vo(2) peak and VT as well as four 8-minute submaximal workbouts for the determination of RV(VO(2)) and RV(HRT). One-way repeated-measures analysis of variance indicated that there were no significant (p > 0.05) mean differences among the running velocities for the RV(VO(2)), RV(HRT), and VT. The results of this study indicated that the mathematical model used to estimate PWC(VO(2)) and PWC(HRT) for cycle ergometry could be applied to treadmill running. Furthermore, the RV(VO(2)) and RV(HRT) test may provide submaximal techniques for estimating the VT.

Adult↗

PubMed2006

Regulation of corticotropin-releasing factor and its types 1 and 2 receptors by leptin in rats subjected to treadmill running-induced stress.

The present study was conducted to investigate the long-term effects of subchronic elevation of central leptin levels on the expression of corticotropin-releasing factor (CRF) and its types 1 and 2 receptors in the brain of rats subjected to treadmill running-induced stress. PBS or recombinant murine leptin was infused continuously for a period of 5 days into the third ventricle of rats with the aid of osmotic minipumps at a delivery rate of 2 mug/day. On the fifth day of infusion, rats were killed under resting conditions or after a session of treadmill running, which is known to induce a stress response in rats. Leptin treatment significantly decreased food intake, body weight, white adipose tissue weight, glucose and insulin plasma contents, and blunted the treadmill running-induced elevation in plasma levels of corticosterone. Leptin infusion prevented stress-induced de novo synthesis of CRF in the paraventricular hypothalamic nucleus (PVN), which was measured using the intronic probe for CRF heteronuclear RNA. The induction of the type 1 CRF receptor (CRF(1)R) in the PVN and supraoptic nucleus in running rats was also significantly blunted by leptin. In contrast, leptin treatment strongly increased the expression of type 2 CRF receptor (CRF(2)R) in the ventromedial hypothalamic nucleus (VMH). The present results suggest that subchronic elevation of central levels of leptin blunts treadmill running-induced activation of the hypothalamic-pituitary-adrenal axis through the inhibition of activation of the CRFergic PVN neurons, and potentially enhances the anorectic CRF effects via the stimulation of expression of CRF(2)R in the VMH.

Adipose Tissue↗

PubMedDate not supplied

Running shoes, orthotics, and injuries.

Running is the most visible expression of the continued interest in regular physical activities. Unfortunately injuries are common, primarily due to overuse, and a number of aetiological factors have been recognised. Of these, training errors can be responsible for up to 60% of injuries. The training surface, a lack of flexibility and strength, the stage of growth and development, poor footwear and abnormal biomechanical features have all been implicated in the development of running injuries. A thorough understanding of the biomechanics of running is a necessary prerequisite for individuals who treat or advise runners. Clinically, the configuration of the longitudinal arch is a valuable method of classifying feet and has direct implications on the development and management of running problems. The runner with excessively pronated feet has features which predispose him/her to injuries that most frequently occur at the medial aspect of the lower extremity: tibial stress syndrome; patellofemoral pain syndrome; and posterior tibialis tendinitis. These problems occur because of excessive motion at the subtalar joint and control of this movement can be made through the selection of appropriate footwear, plus orthotic foot control. The runner with cavus feet often has a rigid foot and concomitant problems of decreased ability to absorb the force of ground contact. These athletes have unique injuries found most commonly on the lateral aspect of the lower extremity: iliotibial band friction syndrome; peroneus tendinitis; stress fractures; trochanteric bursitis; and plantar fasciitis. Appropriate footwear advice and the use of energy-absorbing materials to help dissipate shock will benefit these individuals. Running shoes for the pronated runner should control the excessive motion. The shoes should be board-lasted, straight-lasted, have a stable heel counter, extra medial support, and a wider flare than the shoes for the cavus foot. For these athletes a slip-lasted, curve-lasted shoe with softer ethylene vinyl acetate (EVA) and a narrow flare is appropriate. Orthotic devices are useful in selected runners with demonstrated biomechanical abnormalities that contribute to the injury. Soft orthotics made of a commercial insole laminated with EVA are comfortable, easily adjusted, inexpensive, and more for-giving than the semirigid orthotics which are useful in cases where the soft orthotic does not provide adequate foot control. A review of injury data shows an alarming rise in the incidence of knee pain in runners-from 18% to 50% of injuries in 13 years.(ABSTRACT TRUNCATED AT 400 WORDS)

Athletic Injuries↗

PubMed1988

Metabolic and hormonal changes in IDDM during long-distance run.

Hormonal and metabolic changes were compared in five insulin-dependent diabetic men and five control men during a 3-h marathon-training run. Insulin was withheld 16-26 h before the start of the run, and a normal breakfast was finished 2.5 h before the start of the run. Blood glucose concentrations decreased significantly in the diabetic subjects but remained constant in the control subjects. During the run, plasma free fatty acids, beta-hydroxybutyrate, and alanine concentrations behaved similarly in both groups. Only postexercise ketosis was more pronounced in the diabetic subjects. Peripheral serum free-insulin concentrations were slightly lower in the diabetic subjects at the start of the study, but these insulin concentrations became significantly elevated afterward compared with the control subjects. Plasma glucagon levels increased in the diabetic but not in the control subjects. Growth hormone levels increased sharply and to significantly higher levels in the diabetic than in the control subjects, who presented a slow gradual increase. Plasma cortisol levels were slightly, but at some moments significantly, higher in the diabetic subjects. The plasma catecholamine concentrations increased in both groups but to significantly higher levels in the diabetic subjects. There is no evidence from this study for an insufficient secretion of counterregulatory hormones if a hypoglycemic reaction occurs during a long-distance run in reasonably well controlled, well-trained diabetic subjects without long-term complications.

Adult↗

PubMed1999

Timing in relay running.

Skillful performance in relay running requires that the athlete who is to take possession of the baton meets the baton carrier before reaching the end of the transmission zone while running at the highest speed possible. In the present study we examined the effects of variations in approach speed on the running behavior of the receiver. Kinematic analyses indicated that receivers regulated both the moment of initiation as well as the accelerative characteristics of their run. Contrary to the instructions given, baton carriers adapted their running speed as well to ensure a safe passage, making it difficult for the receiver to evaluate the appropriateness of their behavior.

Acceleration↗

PubMed1999

Physiological measurements of walking and running in people with transtibial amputations with 3 different prostheses.

STUDY DESIGN: A 3-factor (foot type, speed, and mode of ambulation) repeated-measures experimental design was used. OBJECTIVES: To compare the differences in energy expenditure, gait efficiency, and relative exercise intensity in persons with transtibial amputations with various prostheses. BACKGROUND: There is a need for improved prosthetic designs to accommodate physically active persons with lower-extremity amputations. METHODS AND MEASURES: We used progressive speeds of treadmill walking (53.64, 67.05, 80.46, 93.87, and 107.28 m/min) and running (120.69, 134.1, and 147.51 m/min) with 3 different types of prostheses: the Solid Ankle Cushion Heel (SACH) foot, the Flex-Foot (FF), and the Re-Flex Vertical Shock Pylon (VSP) prosthesis. Five physically active men with unilateral transtibial amputations served as subjects (aged 31.6 +/- 4.28 years). RESULTS: The following statistically significant differences (improvements) between the Re-Flex VSP versus the FF and the SACH foot were found. Energy cost: walking (5%), running (11%); gait efficiency: walking (6%), running (9%); relative exercise intensity: walking (4%), running (5%). However, we found no significant differences between the FF and the SACH. CONCLUSIONS: The Re-Flex VSP appears to have a positive effect on energy cost, efficiency, and relative exercise intensity compared with the other prosthetic foot types during walking and running.

Adult↗

PubMed1994

Heat exhaustion in The Sun-Herald City to Surf fun run.

OBJECTIVE: To investigate the relationship between motivational factors and physical and biological causes of heat exhaustion in fun run entrants. DESIGN AND SETTING: Case-control study, The Sun-Herald City to Surf fun runs in Sydney in 1991 and 1992. PARTICIPANTS: There were 63,732 race entrants who completed the run and received a finishing time; 79 runners with heat exhaustion and 310 age, sex and performance matched controls were enrolled in the study. MAIN OUTCOME MEASURE: A diagnosis of heat exhaustion was made if a runner collapsed and, when first receiving medical care, had a rectal temperature of 38 degrees C or higher. RESULTS: Two readily identifiable groups of runners were at high risk of heat exhaustion--accomplished non-élite (preferred) runners and runners of good ability (Group A). The attack rate was highest among accomplished non-élite runners, but a combination of a relatively high rate and the large number of entrants in Group A runners accounted for most cases. Four major risk factors for heat exhaustion were identified: motivation to exceed previous performance targets; failure to drink fluids during the run; failure of trained runners to acclimatise for the race by training in the warmer parts of the day; and previous history of heat exhaustion. CONCLUSION: Information from this investigation will enable more effective targeting of educational prevention programs in The Sun-Herald City to Surf fun run and provide baseline data for monitoring the effectiveness of these programs to modify high risk behaviour by participants.

Adolescent↗

PubMed2004

[Analysis of sports hematuria after running in summer].

BACKGROUND: The recent sport promotion and healthy boom brought increasing the sport population. Running especially is the most popular activity. Various urinary abnormalities are induced by strenunous exercise. Hematuria has been found after various sports activities and noted as sports hematuria by some studies. We evaluated relation between hematuria and running as the most popular sport in summer. MATERIAL AND METHODS: Urine samples were obtained from 109 healthy volunteers participated in 5 km run, at rest before and immediately after running. We could evaluate 90 of all and investigate counts and morphpology of urinary red cells by microscopic finding of urine sediments and analysis of flowcytometry for urinary cells. RESULTS: Eighty-three subjects had increased counts of urinary red cells after running. Of these, 32 had counts above the normal range, microscopic hematuria (RBC above 3/hpf). In analysis of these 32 had dysmorphic pattern mostly. CONCLUSION: This study confirms that exercise induces hematuria easily and sports hematuria has a glomerular source chiefly.

Adult↗

PubMed1999

Combined caffeine and ephedrine ingestion improves run times of Canadian Forces Warrior Test.

The ingestion of a combination of caffeine (C) and ephedrine (E) has been reported to prolong exercise time to exhaustion during cycle ergometry at 85% VO2max. The present study was undertaken to investigate whether this enhancement would occur in a field setting and if drug ingestion on 1 d would affect performance 1 d later. Two hours after ingesting either a combination of 375 mg of C and 75 mg E (C+E), or a placebo (P), 9 healthy male recreational runners completed six balanced and double-blind trials of the Canadian Forces Warrior Test (WT), a 3.2 km run wearing "fighting order" which weighed about 11 kg. The trials were performed in sets of two runs, i.e., two runs were done 24 h apart, and these sets were separated by a minimum of 7 d. The sets were: C+E trial on day 1 (D1), placebo on day 2 (P2); placebo first (P1), C+E second (D2); and placebo first (P3), placebo second (P4). In addition, 1 wk before the treatment trials the subjects performed a control trial WT. During the WT, heart rates (HR) were recorded every minute. Plasma C and E levels immediately before the WT were similar for both C+E trials, but were undetectable for all P trials. Run times (mean+/-SD) were 15.3+/-0.6, 15.4+/-0.9, 15.5+/-1.2, 15.4+/-0.9, 15.4+/-0.9, 14.8+/-0.7, and 14.6+/-0.8 min for control, P1, P2, P3, P4, D1, D2 trials, respectively. The two C+E trial run times were similar and both were significantly faster (p < 0.05) than control and all placebo trials. HR during the WT was significantly higher (p < 0.05) for the C+E trials compared with the other trials. WT performance was not impaired by C+E ingestion 24 h earlier. In conclusion, performance of the WT was improved by ingestion of C+E.

Adult↗

PubMed2000

Pre-exercise carbohydrate and fluid ingestion: influence of glycemic response on 10-km treadmill running performance in the heat.

BACKGROUND: The purpose of this study was to determine the influence of ingesting solutions containing mixtures of carbohydrate (CHO) types on pre-exercise glycemic response, exercise-induced hypoglycemia, metabolic responses, and 10-km treadmill running performance in a warm environment. METHODS: Ten trained runners completed 6, self-paced 10-km treadmill runs one hour after ingesting 900 ml of one of the following test solutions: a water placebo (WP), an 8 g 100 ml-1 high fructose corn syrup solution (HFG; 72 g CHO), a 6 g 100 ml-1 glucose solution (GLU; 54 g CHO), a 6 g.100 ml-1 sucrose/glucose mixture (SUG; 54 g CHO), or banana with water to equal 900 ml (BAN; approx. 54 g CHO). The sixth condition was 675 ml of an 8 g.100 ml-1 HFCS solution (LFG; 54 g CHO). Blood samples were taken prior to ingestion and every 15 min during rest and at 15 and 30 min, and at the end of the 10-km run. Blood was analyzed for glucose (BG) insulin (IN), glycerol, lactate, and percent change in plasma volume. Urine volume during the 1 hour of rest and change in body mass during exercise were also determined. RESULTS: A significant (p < 0.05) correlation (r = -0.684) was seen between the pre-exercise glycemic response (PEGR = area under the resting BG curve) and the change in BG from pre-EX to 15 min of exercise. BG at 15 min of exercise was significantly higher in the WP (5.22 mM) versus the other conditions (HFG = 3.32, LFG = 3.91, GLU = 3.38, BAN = 3.74 & SUG = 3.63 mM). Pre-exercise IN was lower in the WP (6.54 U ml-1) condition versus the other conditions (HFG = 22.1, LFG = 16.2, GLU = 23.3, BAN = 18.8 & SUG = 12.8 U.ml-1). Ten km performance times were not different (WP = 41.87, HFG = 41.66, LFG = 41.79, GLU = 41.65, BAN = 41.53, and SUG = 41.75 min). A significantly greater body mass loss occurred due to urine production during the 60 min of rest in the WP compared to the other conditions. The degree of exercise-induced decline in blood glucose was related to the PEGR; however, the decline in BG did not affect 10-km running performance. In addition, there were no differences in the metabolic responses during exercise between the different CHO types, nor did the type of CHO influence running performance. Finally, the presence of CHO and/or electrolytes in the hydration solutions produced a better fluid retention during the 60-min pre-exercise rest period compared to water. CONCLUSIONS: The results confirmed that if a competitive athlete consumed a breakfast prior to ingesting a CHO-electrolyte beverage, a practice that is common, the glycemic responses may be different.

Adult↗