The physiological effects of cycling on tandem and single bicycles.

OBJECTIVE: The purpose of this field study was to compare the physiological responses from cycling on a tandem road bicycle to those from cycling on a single road bicycle. METHODS: Nine pairs of experienced, recreational tandem cyclists rode a tandem or their single bicycle for 5 min at each velocity of 19.3, 22.5, 25.8, and 29.0 kph on a flat, paved surface. Heart rate (HR), rating of perceived exertion (RPE), and lactic acid (LA) data were collected after each interval. RESULTS: Riding a tandem resulted in lower HR, RPE, and LA mean values across the four velocities compared to the single bicycle. Mean (SD) HR, RPE, and LA for tandem and single bicycles were 126 (20.7) v 142 (20.1) bpm, 10.1 (1.7) v 11.3 (2.6), and 1.46 (1.0) mM/L v 2.36 (1.7) mM/L, respectively. No position differences were observed between the captain and stoker (front and rear positions) when both were on the tandem. Stokers had significantly lower HR, LA, and RPE values when they rode a tandem compared to a single bicycle. No statistical differences were observed between bicycles for the captains. When on the single bicycle, captains exhibited significantly lower HR, RPE, and LA values than stokers. CONCLUSION: Cycling on a tandem resulted in lower physiological stress than when cycling at the same velocity on a single bicycle. Cyclists were able to ride from 4.8-8.0 kph faster on a tandem than on a single bicycle at similar physiological stress. Apparently, stokers can add to power output on a tandem without adding significantly to wind resistance.

The physiological effects of beverage ingestion during cross country ski training in elite collegiate skiers.

The purpose of this study was to investigate the effects of beverage ingestion on fluid balance during 1.5 hr of low intensity cross country skiing. In Part I, 6 skiers drank water ad libitum during ski training. In Part II, 10 skiers were matched by body weight (BW) and assigned to ingest 2.5 ml.kg-1 BW of water or a carbohydrate/electrolyte (CE) beverage every 2.5 km. Skiing speed averaged 11.5 km.hr-1 for 90 min around a 5 km groomed track. Following 20 min of seated rest, blood samples were collected immediately before and approximately 30 min after skiing. Part I data indicated that subjects ingested 576 +/- 189 ml of fluid and produced 266 +/- 205 ml of urine; BW, plasma and urine osmolality, and plasma protein decreased significantly. In Part II, the CE group produced less urine (135u75 vs. 450 +/- 262 ml) and had smaller decreases in plasma osmolality (-1.0 +/- 1.0 vs. -7.0 +/- 2.4 mOsm.kg H2O) and protein (-0.11 +/- 08 vs. -0.42 +/- 0.24 gL-1) than the water group. No differences were observed for BW loss, % change in PV, FWC, or change in urine osmolality. It was concluded that ad lib water ingestion was inadequate to minimize fluid balance disruption. Plain water ingestion also led to significant dilution of the plasma and increased urine output. However, the ingestion of CE led to attenuation of fluid balance disruption, presumably due to the maintenance of osmotic balance in the plasma.

The effects of mountain bike suspension systems on energy expenditure, physical exertion, and time trial performance during mountain bicycling.

The purpose of this 3-Phase study was to investigate the effects of suspension systems on muscular stress, energy expenditure, and time trial performance during mountain biking. Three suspension systems were tested, a rigid frame bike (RIG), a suspension fork bike (FS), and a front and rear suspension bike (FSR). Phase I and II consisted of cycling at 16.1 km.hr-1 over a flat, bumpy course for 63 min. Phase III consisted of ascending (ATT), descending (DTT), and cross country (XTT) time trials. Phase I assessed muscular stress by 24 h change in CK, Phase II assessed HR, VO2, VE, and Phase III assessed performance responses to the suspension systems. The 24 hr change in CK was greater for RIG than FS and FSR (+91.9 +/- 79.5 IU vs +8.6 +/- 17.5 IU and +9.7 +/- 21.8 IU). Mean HR was greater for RIG than FS and FSR (153.7 +/- 15.6 bpm vs 146.7 +/- 15.4 bpm, 146.3 +/- 16.2 bpm). Subjects rode significantly faster on FS than FSR and RIG during the XTT (30.9 +/- 2.0 min vs 32.3 +/- 3.6 min, 32.3 +/- 3.2 min). Subjects RPE was lower for FSR than FS and RIG, however, no differences were observed for VO2, VE, ATT, or DTT. Cyclists incurred less muscular stress, indicated by CK and HR, when riding the FS and FSR. Although the FS and FSR weigh from 0.7 to 2.2 kg more than RIG, no differences were observed for energy expenditure and that riding the FS in a XTT resulted in a faster finishing time than FSR or RIG.

Effect of carbohydrate ingestion on performance of non-fasted cyclists during a simulated 80-mile time trial.

The purpose of this study was to determine the effect of carbohydrate supplementation on finishing time of a realistically simulated 80 mile bicycle time trial. Fourteen trained cyclists pedalled at self-selected pace on their own bicycles on windload simulators. Two trials were performed one week apart. Each trial was preceded by two days of prescribed diet, with a final feeding 3-4 h prior to exercise. Following each 10 mile segment, subjects ingested either a non-caloric placebo (PL) or the carbohydrate maltodextrin supplement (MD; 5% maltodextrin +2% fructose) at dosage of 0.25 g.kg-1 body weight (mean intake rate, total: 37 g.h-1, 148 g) in a double blind, counter-balanced design. Mean (+/- SEM) finishing times were faster by 5% with MD (241.0 +/- 2.1 minutes versus 253.2 +/- 2.1 minutes), p < 0.05. With MD, serum glucose levels rose sharply after 40 miles and were significantly higher than PL (p < 0.05). Final glucose values were 6.0 +/- 0.2 mmol.l-1 and 4.1 +/- 0.2 mmol.l-1 for MD and PL, respectively. With MD, free fatty acid levels were significantly lower (p < 0.05), and riders sustained higher average intensity over the entire distance. At the finish, intensities were 64.7 +/- 1.9% VO2max and 55.3 +/- 1.9% VO2max for GP and PL, respectively. Mean carbohydrate oxidation was significantly higher (p < 0.05) for MD, 2.01 +/- 0.2 g.min-1 and 1.64 +/- 0.2 g.min-1 for MD and PL, respectively. These data show that ingestion of MD, during ultraendurance exercise, in comparison to PL, decreases the time to finish a self-paced bicycle time trial.

Glycemic and insulinemic response to preexercise carbohydrate feedings.

The effects of preexercise hyperinsulinemia on exercising plasma glucose, plasma insulin, and metabolic responses were assessed during 50 min cycling at 62% VO2max. Subjects were fed a 6% sucrose/glucose solution (LCHO) or a 20% maltodextrin/glucose solution (HCHO) to induce changes in plasma insulin. During exercise, subjects assessed perceived nauseousness and light-headedness. By the start of exercise, plasma glucose and plasma insulin had increased. In the LCHO trial, plasma glucose values significantly decreased below the baseline value at 30 min of exercise. However, by 40 min, exercise plasma glucose and insulin values were similar to the baseline value. Exercise plasma glucose and insulin did not differ from baseline values in the HCHO trial. Ingestion of LCHO or HCHO was not associated with nausea or lightheadedness. It was concluded that the hyperinsulinemia induced by preexercise feedings of CHO did not result in frank hypoglycemia or adversely affect sensory or physiological responses during 50 min of moderate-intensity cycling.

Physiological responses to glycerol ingestion during exercise.

To study selected cardiovascular, thermoregulatory, and hormonal responses to the consumption of glycerol solutions during exercise, nine subjects cycled for 90 min at 50% peak O2 uptake in a 30 degree C, 45% relative humidity environment. Beverages tested included a 10% glycerol solution (G), a 6% carbohydrate-electrolyte beverage (CE), the 6% carbohydrate-electrolyte beverage plus 4% glycerol (CEG), and a water placebo (WP) ingested at regular intervals during the first 60 min of exercise. The beverages were administered in counterbalanced order with subjects serving as their own controls. Ingestion of the glycerol solutions resulted in an increase in plasma osmolality and attenuation of the decrease in plasma volume associated with the WP treatment (P less than 0.05). Plasma renin activity was highest with WP (P less than 0.05), and G was associated with increased antidiuretic hormone levels (P less than 0.05). Ratings of perceived thirst were lowest for CEG and G, and the frequency of gastrointestinal distress was greatest for G (P less than 0.05). However, no differences among beverage treatments were observed for heart rate, esophageal temperature, sweat rate, ratings of perceived exertion, or changes in cortisol and aldosterone levels. These data indicate that there are no substantial metabolic, hormonal, cardiovascular, or thermoregulatory advantages to the consumption of solutions containing 4 or 10% glycerol during exercise.

Responses to varying rates of carbohydrate ingestion during exercise.

The purpose of this study was to determine how the ingestion of carbohydrate at varying rates influences physiological, sensory, and performance responses to prolonged exercise at 65-75% VO2max. Ten subjects ingested either a water placebo (WP) or carbohydrate solutions formulated to provide glucose at the rates of 26, 52, and 78 g, h-1 during 2 h of cycling exercise in a cool (10 degrees C) environment. Beverages were administered in a double-blind, counterbalanced design. A 4.8 km performance test followed each 2 h session. The average time required to complete the performance test was less with the carbohydrate feedings than with WP: mean (+/- SE) for WP = 505.0 +/- 18.7 s. 26 g.h(-1) = 476.0* +/- 8.8 s. 52 g.h(-1) = 483.8 +/- 12.7 s. 78 g.h(-1) = 474.3* +/- 19.1 s; *P less than 0.05 vs WP. Carbohydrate feeding resulted in higher plasma glucose and insulin, and lower free fatty acid concentrations than did WP. Changes in plasma osmolality, plasma volume, rectal temperature, lactate, heart rate, respiratory exchange ratio, ratings of perceived exertion, and sensory responses were similar among beverage treatments. Compared with WP, ingestion of the glucose beverages minimized changes in plasma ACTH and cortisol. In summary, carbohydrate feeding at the rates of 26 and 78 g.h(-1) was associated with improved exercise performance. The data further indicate that a dose-response relationship does not exist between the amount of carbohydrate consumed during exercise and exercise performance.

The effects of glucose, fructose, and sucrose ingestion during exercise.

The purpose of this study was to compare the physiological, sensory, and exercise performance responses to ingestion of 6% glucose, 6% fructose, and 6% sucrose solutions during cycling exercise. Twelve subjects completed three sessions consisting of 115 min of intermittent cycle ergometer exercise at 65-80% of VO2max followed by a timed performance bout requiring the completion of 600 pedal revolutions. During each of five 4-min rest periods, subjects consumed 3 ml.kg LBM-1 of one of the beverages. Beverages were presented in counterbalanced, double-blind fashion. Heart rate, VO2, plasma urate, plasma lactate, respiratory exchange ratio, and carbohydrate combustion rates changed similarly among beverage treatment. However, fructose was associated with lower plasma glucose and serum insulin, a larger loss of plasma volume, greater gastrointestinal distress and relative perceived exertion ratings, and higher plasma or serum concentrations of free fatty acids, fructose, and cortisol values than sucrose or glucose (P less than 0.05). Compared to sucrose and glucose, fructose feeding also resulted in lower lactate and HR values during the performance bout (P less than 0.05). Mean +/- SE cycling performance times were faster with sucrose and glucose than with fructose: 419.4 +/- 21.0 s, 423.9 +/- 21.2 s, and 488.3 +/- 21.1 s, respectively (P less than 0.05). Relative to 6% solutions of sucrose and glucose, ingestion of a 6% fructose beverage is associated with gastrointestinal distress, compromised physiological response, and reduced exercise capacity.

Carbohydrate feeding and exercise: effect of beverage carbohydrate content.

The purpose of this study was to determine the effect of ingesting fluids of varying carbohydrate content upon sensory response, physiologic function, and exercise performance during 1.25 h of intermittent cycling in a warm environment (Tdb = 33.4 degrees C). Twelve subjects (7 male, 5 female) completed four separate exercise sessions; each session consisted of three 20 min bouts of cycling at 65% VO2max, with each bout followed by 5 min rest. A timed cycling task (1200 pedal revolutions) completed each exercise session. Immediately prior to the first 20 min cycling bout and during each rest period, subjects consumed 2.5 ml.kg BW-1 of water placebo (WP), or solutions of 6%, 8%, or 10% sucrose with electrolytes (20 mmol.l-1 Na+, 3.2 mmol.l-1 K+). Beverages were administered in double blind, counterbalanced order. Mean (+/- SE) times for the 1200 cycling task differed significantly: WP = 13.62 +/- 0.33 min, *6% = 13.03 +/- 0.24 min, 8% = 13.30 +/- 0.25 min, 10% = 13.57 +/- 0.22 min (* = different from WP and 10%, P less than 0.05). Compared to WP, ingestion of the CHO beverages resulted in higher plasma glucose and insulin concentrations, and higher RER values during the final 20 min of exercise (P less than 0.05). Markers of physiologic function and sensory perception changed similarly throughout exercise; no differences were observed among subjects in response to beverage treatments for changes in plasma concentrations of lactate, sodium, potassium, for changes in plasma volume, plasma osmolality, rectal temperature, heart rate, oxygen uptake, rating of perceived exertion, or for indices of gastrointestinal distress, perceived thirst, and overall beverage acceptance.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum and urinary markers of skeletal muscle tissue damage after weight lifting exercise.

The purpose of this study was to determine whether high intensity weight lifting exercise produces elevations of urinary 3-methylhistidine (3-MH), serum creatine kinase activity (CK), and serum myoglobin concentration (MY), and whether trained weight lifters differed in such responses when compared to a group of untrained subjects. Ten experienced male weight lifters (EWL) and seven untrained male subjects (IWL) performed three sets of six weight lifting exercises at 70%-80% of 1 RM. All subjects consumed a meat-free diet. The 3-MH:creatinine (3-MH:CR) values decreased 24 h and 48 h following exercise (P less than 0.05). The 12-h and 24-h postexercise CK response and the 12-h postexercise MY response increased for both EWL and IWL (P less than 0.05). However, EWL had a lower 24-h postexercise CK response and lower 12-h and 24-h postexercise MY responses compared to IWL (P less than 0.05). Within 48 h following weight lifting exercise, skeletal muscle protein degradation (as assessed by 3-MH:CR values) decreased regardless of prior training experience whereas skeletal muscle tissue damage (as assessed by CK and MY responses) increased. However, prior weight lifting training appeared to diminish the extent of muscle tissue damage.

The effect of fluid and carbohydrate feedings during intermittent cycling exercise.

The purpose of this study was to determine the effect of ingesting water or carbohydrates solutions on physiologic function and performance during 1.6 h of intermittent cycling exercise in the heat (dry bulb temperature = 33 degrees C). Thirteen male subjects (24 to 35 yr) completed four separate rides. Each ride consisted of intermittent steady-state cycling (at 55 and 65% VO2max) interspersed with five rest periods. A timed 480 revolution cycling task completed each experimental session. During each rest period, subjects consumed 2 ml.kg-1 body weight of water placebo or solutions of 5% glucose polymer, 6% sucrose/glucose, or 7% glucose polymer/fructose. Beverages were administered in double-blind, counter-balanced order. No differences were observed among subjects in response to beverage treatments for changes in plasma concentrations of total proteins, sodium, potassium, lactate, or in osmolality, percent change in plasma volume, heart rate, oxygen uptake, respiratory exchange ratio, rating of perceived exertion, sweat rate, rectal temperature, or mean skin temperature. Compared to water placebo, the carbohydrate treatments produced higher plasma glucose values following 1 h cycling (P less than 0.01). Mean (SD) times for the 480 revolution cycling task: water placebo = 432 (43) s; glucose polymer = 401 (52) s; *sucrose/glucose = 384 (39) s; and *glucose polymer/fructose = 375 (30) s, where = P less than 0.001 compared to water placebo. Physiologic function was similarly maintained during exercise by all beverage treatments, while ingestion of sucrose/glucose and glucose polymer/fructose resulted in improved end-exercise cycling performance.