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Biomedical subjects

A C Snyder

Publications and source records attributed to A C Snyder.

At least 19 recordsLinked to original sources
PubMed1999

Evidence for restricted muscle blood flow during speed skating.

INTRODUCTION: We have previously hypothesized restricted muscle blood flow during speed skating, secondary to the high intramuscular forces intrinsic to the unique posture assumed by speed skaters and to the prolonged duty cycle of the skating stroke. METHODS: To test this hypothesis, we studied speed skaters (N = 10) during submaximal and maximal cycling and in-line skating, in both low (knee angle = 107 degrees) and high (knee angle = 112 degrees) skating positions (CE vs SkL vs SkH). Supportive experiments evaluated muscle desaturation and lactate accumulation during on-ice speed skating and muscle desaturation during static exercise at different joint positions. RESULTS: Consistent with the hypothesis were reductions during skating in VO2peak (4.28 vs 3.83 vs 4.26 L x min(-1)), the VO2 at 4 mmol x L(-1) blood lactate (3.38 vs 1.93 vs 3.31 L x min(-1)), and cardiac output during maximal exercise (33.2 vs 25.3 vs 25.6 L x min(-1)). The reduction in maximal cardiac output was not attributable to differences in HRmax (197 vs 192 vs 193 b x min(-1)) but to a reduction in SVmax (172 vs 135 vs 134 mL x beat(-1)). The reduction in SV appeared to be related to an increased calculated systemic vascular resistance (354 vs 483 vs 453 dynes x s(-1) x cm(-1)). During maximal skating there was also a greater % O2 desaturation of the vastus lateralis based on near infrared spectrophotometry (50.3 vs 74.9 vs 60.4% of maximal desaturation during cuff ischemia). The results were supported by greater desaturation with smaller knee angles during static exercise and by greater desaturation and accelerated blood lactate accumulation during on-ice speed skating in the low vs high position. The results of this study support the hypothesis that physiological responses during speed skating are dominated by restriction of blood flow, attributable either to high intramuscular forces, the long duty cycle of the skating stroke, or both.

Adult↗
PubMed1998

Physiological effects of technique and rolling resistance in uphill roller skiing.

OBJECTIVE: The double pole technique (DP) has been shown to be more economical than the V1 skate technique (V1 ) on flat terrain. The objective of the present study was to compare these two techniques during uphill roller skiing. In addition, the physiological effects of changing roller ski rolling resistance was examined for V1. METHODS: Five female and five male competitive cross-country skiers roller skied 4-min bouts on a 5.2% incline while physiological measurements were made. RESULTS: Oxygen uptake (VO2) values averaged 8% greater (P = 0.0004) with V1, whereas rating of perceived exertion (RPE) and blood lactate concentrations were higher (P < or = 0.002) with DP. Doubling the dynamic friction coefficient of the roller skis, which increased external power output by 16-17%, resulted in VO2 values with V1 that averaged 13% higher (P = 0.0006). This magnitude of change in roller ski rolling resistance did not cause a statistical change in the relationship of VO2 with RPE. CONCLUSIONS: These findings suggest that 1) grade has little effect on relative economies of DP and V1, possibly because of a lower effectiveness of force application with V1 when going uphill, and 2) large differences in roller ski rolling resistance should have no effect on the cardiovascular training adaptations that result from uphill roller skiing with V1.

Adult↗
PubMed1998

Overtraining and glycogen depletion hypothesis.

Low muscle glycogen levels due to consecutive days of extensive exercise have been shown to cause fatigue and thus decrements in performance. Low muscle glycogen levels could also lead to oxidation of the branched chain amino acids and central fatigue. Therefore, the questions become, can low muscle glycogen not only lead to peripheral and central fatigue but also to overtraining, and if so can overtraining be avoided by consuming sufficient quantities of carbohydrates? Research on swimmers has shown that those who were nonresponsive to an increase in their training load had low levels of muscle glycogen and consumed insufficient energy and carbohydrates. However, cyclists who increased their training load for 2 wk but also increased carbohydrate intake to maintain muscle glycogen levels still met the criteria of over-reaching (short-term overtraining) and might have met the criteria for overtraining had the subjects been followed for a longer period of time. Thus, some other mechanism than reduced muscle glycogen levels must be responsible for the development and occurrence of overtraining.

Athletic Injuries↗
PubMed1996

Athletic performance in relation to training load.

Athletic performance generally is thought to improve with increases in training load. However, few data exist showing the quantitative relationship between training load and performance. We followed 56 athletes (16 runners; 40 cyclists/speed skaters) during 12 weeks of training. We recorded index performances (3.2 km time trial or 5 or 10 km bicycle ergometry) after 6 weeks of baseline training and 6 weeks of a self-selected training increases. Training load was quantitated as the product of intensity (global rating of perceived exertion (RPE)) and the duration (time) of each training session. Load was expressed as the weekly average over the 6 weeks preceding each index performance. We also recorded the duration of high intensity training (RPE>5, hard) (inten). From 6 to 12 weeks, performance improved 12.95 +/- 3.83 to 12.66 +/- 3.00 min (p < .01). Training time (345 +/- 282 to 355 +/- 273 min/wk) and inten (61 +/- 88 to 71 +/- 91 min/wk) did not change significantly, although RPE (3.8 +/- 0.7 to 4.0 +/- 0.8) and load (1242 +/- 957 to 1386 +/- 978) increased significantly. No strong correlations existed between changes in performance and changes in any training measure (TIME, r = -0.031, RPE, r = -0.039, LOAD, r = 0.29, INTEN, r = 0.025.) Data suggest that improved performance in events of 7-20 minutes duration in response to intensified training is primarily dependent upon increases in total load and overall RPE during training and; that a 10-fold increase in training load may be associated with an approximately 10% improvement in performance. These data suggest the possibility of understanding the training responses of athletes on a quantitative basis.

Adult↗
PubMed1995

Effects of specific versus cross-training on running performance.

The cross-training (XT) hypothesis suggests that despite the principle of specificity of training, athletes may improve performance in one mode of exercise by training using another mode. To test this hypothesis we studied 30 well-trained individuals (10 men, 20 women) in a randomized longitudinal trail. Subjects were evaluated before and after 8 weeks of enhanced training (+10%/week), accomplished by adding either running (R) or swimming (XT) to baseline running, versus continued baseline running (C). Both R (-26.4s) and XT (-13.2s) improved time trial (3.2 km) performance, whereas C did not (-5.4s). There were no significant changes during treadmill running in maximum oxygen uptake (VO2peak; -0.2, -6.0, and +2.7%), steady state submaximal VO2 at 2.68 m.s-1 (-1.2, -3.3 and +0.2 ml.kg-1.min-1), velocity at VO2peak (+0.05, +0.25 and +0.09 m.s-1) or accumulated O2 deficit (+11.2, -6.1 and +9.4%) in the R, XT or C groups, respectively. There was a significant increase in velocity associated with a blood lactate concentration of 4 mmol.l-1 in R but not in XT or C (+0.32, +0.07 and +0.08 m.s-1). There were significant changes in arm crank VO2peak (+5%) and arm crank VO2 at 4 mmol.l-1 (+6.4%) in XT. There was no significant changes in arm crank VO2peak (+1.3 and -7.7%) or arm crank VO2 at 4 mmol.l-1 (+0.8 and +0.4%) in R or C, respectively. The data suggest that muscularly non-similar XT may contribute to improved running performance but not to the same degree as increased specific training.

Adult↗
PubMed1995

Overtraining following intensified training with normal muscle glycogen.

The purpose of this study was to determine if consumption of appropriate amounts of carbohydrate during a period of increased exercise training would protect the athletes from becoming overtrained. Eight male competitive cyclists were monitored and tested during three training periods: a) normal training (moderate intensity, long duration, 7 d, NORM); b) overtraining (high intensity training, 15 d, OVER); and c) recovery (minimal training, 6 d, REC). Throughout the training 160 g of liquid carbohydrate were consumed within the first 2 h after the daily exercise bout. Mean dietary intake (NORM = 13.7 +/- 1.6, OVER = 14.1 +/- 1.0 MJ.d-1) and carbohydrate percent (NORM = 64.0 +/- 2.1, OVER = 67.4 +/- 2.5%) were not different during the different training periods. Similarly, resting muscle glycogen levels were not different (NORM = 530.9 +/- 42.5, OVER = 571.2 +/- 27.5 mumol.g-1 dry weight). Five criteria were used to determine if overtraining occurred in a subject (decreased maximal workload, maximal heart rate, ratio of maximal lactate to rating of perceived exertion (HLa:RPE), and resting plasma cortisol levels, increased affirmative response to a daily questionnaire). All subjects met at least three of the five criteria and thus were classified as overtrained. Therefore, short-term overtraining may occur even when resting muscle glycogen levels are maintained.

Adult↗
PubMed1995

Effect of an abdominal binder during wheelchair exercise.

The purpose of this study was to determine whether use of an abdominal binder would affect oxygen uptake, trunk range of motion, and duration of the stroke phase during wheelchair propulsion. The subjects were six paraplegic wheelchair athletes with T1-T6 injuries and no abdominal muscle function. Each subject performed two trials, one while wearing the binder and one without the binder. Each trial consisted of submaximal and maximal exercise tests conducted on wheelchair rollers. Oxygen uptake was determined by open circuit spirometry while heart rate was determined by telemetry. Max VO2 values averaged 2.51 l.min-1 while average maximum heart rate values were 190 b.min-1. A 3-D video-based motion analysis system was used to obtain kinematic parameters of wheelchair propulsion. In general, 30% of the cycle time was comprised of the stroke phase, while 70% was comprised of the recovery phase across speeds. There were no statistically significant effects of the abdominal binder on any of the cardiovascular or kinematic variables at submaximal or maximal levels of exercise. Under the conditions of this laboratory investigation, it appears that an abdominal binder does not alter physiological or selected biomechanical measures in highly trained athletes.

Abdomen↗
PubMed1995

The bloodless lactate profile.

The blood lactate profile (HLa-P) is an accepted method of evaluating athletes and providing a basis for the prescription of training intensity. For both logistic and public health reasons HLa-P is less than optimal. In this study we evaluate the relative velocity or the %HR-max, obtained during a training session, as alternatives to HLa-P. Competitive speed skaters (N = 20) performed HLa-P consisting of 5.2000 m/400 m at incremental velocities ranging from very slow to maximal (time = 3.0-5.0 min). Blood lactate measured during a 60-s interval following each repetition was used to construct HLa-P and to predict the velocity associated with steady state (HLa = 4.0-6.5 mmol.l-1). Relative velocity was calculated relative to the velocity of the maximal trial. A plot of relative velocity and %HRmax vs HLa demonstrated that HLa = 4.0-6.5 mmol.l-1 occurred at a relative velocity of 78-88% (R2 = 0.807) and at 84-92 %HRmax (R2 = 0.748). In a separate training session the relative velocity and %HRmax models were cross validated by having the subjects skate 9.2000 m/400 m at constant velocity. HLa changes during the training session defined the presence/absence of steady state (delta HLa < 1.0 mM from trial 3 to 9). Comparing the velocity during the training session vs the velocity predicted from HLa-P, relative velocity model and %HRmax model allowed a test of the accuracy of bloodless means of defining steady state. HLa-P correctly predicted 81% of training session HLa responses, the relative velocity model correctly predicted 78%, and the %HRmax model correctly predicted 68%.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

A simplified approach to estimating the maximal lactate steady state.

The exercise intensity associated with an elevated but stable blood lactate (HLa) concentration during constant load work (the maximal steady state, MSS) has received attention as a candidate for the "optimal" exercise intensity for endurance training. Identification of MSS ordinarily demands direct measurement of HLa or respiratory metabolism. The purpose of this study was to test the ability of heart rate (HR) to identify MSS during steady state exercise, similar to that used in conventional exercise prescription. Trained runners (n = 9) and cyclists (n = 12) performed incremental and steady state exercise. MSS was defined as the highest intensity in which blood lactate concentration increased < 1.0 mM from minutes 10 to 30. The next higher intensity workbout completed was defined as > MSS. HR models related to the presence or absence of steady state conditions were developed from the upper 95% confidence interval of MSS and the lower 95% confidence interval of > MSS. Cross validation of the model to predict MSS was performed using 21 running and 45 cycling exercise bouts in a separate group. Using the MSS upper 95% confidence interval model 84% and 76% of workbouts were correctly predicted in cyclists and runners, respectively. Using the > MSS lower 95% confidence interval model, 76% and 81% of workbouts were correctly predicted in cyclists and runners, respectively. Prediction errors tended to incorrectly predict non-steady state conditions when steady state had occurred (16/26) (62%). We conclude that use of these simple HR models may predict MSS with sufficient accuracy to be useful when direct HLa measurement is not available.

Adult↗
PubMed1993

Carbohydrate consumption prior to repeated bouts of high-intensity exercise.

Rapid depletion of muscle glycogen occurs during activities greater than 100% of maximal oxygen uptake. While carbohydrate ingestion prior to an endurance event has been shown to be beneficial, the effects of carbohydrate ingestion on repeated bouts of high-intensity exercise are not known. Therefore, the purpose of this study was to determine if carbohydrate ingestion prior to repeated bouts of high-intensity, short-duration exercise would improve performance. Ten well-trained male cyclists performed two experimental rides, one 15 min after consumption of 5.0 ml.kg-1 body weight of a 19.7% carbohydrate drink and one following a placebo. The experimental ride consisted of four 1.6 km timed performance rides separated by 4.8 km steady-state rides at 80% of maximal oxygen uptake (between the last two performance rides the steady-state rides were 1.6 km at 80% and 1.6 km at 90%). Blood glucose levels were significantly increased following both the ingestion of the carbohydrate beverage and the performance of the exercise bout. Total exercise time following ingestion of the experimental drink [mean (SD); 25.6 (3.3) min] was not different from that following ingestion of the placebo [25.2 (3.3) min]. Similarly, the sum of all four timed performance rides following ingestion of the experimental drink [6.8 (0.9) min] was not different from that following ingestion of the placebo [6.6 (0.9) min]. In the present study, carbohydrate ingestion 15 min prior to exercise increased blood glucose levels, although performance time was not affected.

Adult↗
PubMed1993

A physiological/psychological indicator of over-reaching during intensive training.

Many indicators of over-reaching and over-training have been proposed, using both physiological and psychological techniques. Field testing of athletes has led us to believe that a decrease in the ratio of blood lactate concentration to ratings of perceived exertion indicates a fatigued and/or over-reached state following intensive training. The purpose of this study, therefore, was to test the hypothesis that a decrease in the ratio of blood lactate concentration to ratings of perceived exertion would indicate an over-reached state. Seven well-trained male cyclists performed two weeks each of: normal (moderate) training, overtraining and recovery. During each time period an incremental exercise test was performed to maximal effort with blood lactate concentration (HLa) and ratings of perceived exertion (RPE) obtained for each workload. All seven subjects became over-reached during the two week period of intensive interval training. The ratio of HLa:RPE (multiplied by 100) decreased with all workloads following both one (mean decrease 29.1 +/- 3.0%) and two (mean decrease 48.7 +/- 2.5%) weeks of overtraining. However, only the decrease at the maximal workload was statistically significant. Examining the individual data revealed that at maximal workload all seven subjects had HLa:RPE ratios of less than 100 when over-reached. The ease and speed at which the HLa:RPE ratio can be determined may make it useful for coaches and athletes in monitoring intensive exercise training and recovery.

Adult↗
PubMed1993

Exercise responses to in-line skating: comparisons to running and cycling.

A comparison of the physiological responses to in-line skating with the more traditional modes of exercise training has not been reported. The purpose of this study was to examine the physiological responses to in-line skating compared with running and cycling. Nine trained volunteers (2 male, 7 female) performed 3-6 submaximal (30-90% VO2max) workloads with each exercise mode. Oxygen uptake, heart rate and blood lactate were measured during each trial. Across the spectrum of oxygen uptakes studied, heart rate was higher with in-line skating than with cycling or running. At a lactate concentration of 4 mM, oxygen uptake was less for in-line skating and cycling than for running. Therefore, while in-line skating may be an effective mode of aerobic exercise, the training adaptations for in-line skating at 4 mM lactate may not be as great as for running, and at a given HR may be less than for running and cycling.

Adult↗
PubMed1993

Fixed time versus fixed distance protocols for the blood lactate profile in athletes.

Laboratory studies of blood lactate accumulation often use a fixed time protocol to define the onset (4 mM) of blood lactate accumulation (OBLA) or other indices of blood lactate concentration. For practical reasons, field studies with athletes often use a fixed distance protocol to accomplish the same goal. Whether these variations of protocol are comparable has not been established. We studied 10 subjects in the laboratory during fixed time (4 minute) and fixed distance (2 km) exercise protocols on a racing bicycle attached to a wind load simulator. The fixed distance studies required 3-6 minutes to complete. We also studied the subjects during fixed distance (2 km) rides in the field. In the laboratory there were no systematic differences in the velocity (34.3 4.6 vs 34.2 +/- 4.6 km.hr-1), VO2 (2.78 +/- 0.60 vs 2.84 +/- 0.62 liters.min-1), or heart rate (159 +/- 16 vs 155 +/- 14 beats.min-1) at OBLA in the fixed time vs fixed distance protocols. The correlation coefficients for velocity (r = 0.97), VO2 (r = 0.97) and heart rate (r = 0.94) further indicate the similarity of results. In the field study there was a significant difference in velocity (29.9 +/- 4.8 vs 34.2 +/- 4.6 km.hr-1) but not heart rate (155 +/- 18 vs 155 +/- 15 beats.min-1) at OBLA versus the fixed distance laboratory study. The correlations for velocity (r = 0.47) and heart rate (r = 0.93) support these data. The results suggest that the practical modification of the lactate profile technique of using fixed distance versus fixed time exercise stages does not systematically influence the outcome, at least for exercise stage durations approximating 4 minutes.

Female↗
PubMed1993

Physiological responses during simulated competition.

Laboratory studies with competitive athletes often use graded exercise protocols to elicit physiologic responses. This pattern of power output is different than ordinarily employed by athletes during competition. To understand the physiologic responses during competition, we studied 24 athletes (speed skaters, cyclists, triathletes) during simulated competition, a 5-km time trial on a racing bicycle attached to a windload simulator, and during cycle ergometer graded exercise testing (N = 8). During the time trial the velocity pattern was similar to real world competitions, and the subjects indicated that the time trial was perceptually similar to competition. Physiologic responses were of significantly greater magnitude vs graded exercise (VO2max: 3.46 +/- 0.73 vs 3.27 +/- 0.79 l.min-1; VEmax: 138 +/- 27 vs 119 +/- 22 l.min-1; HRmax 184 +/- 11 vs 175 +/- 11 beats x min-1; HLa 14.8 +/- 3.7 vs 11.9 +/- 2.1 mM). All physiologic measures increased steadily throughout the time trial (km 0, 1, 2, 3, 4, and 5: VO2 = 1.03, 2.95, 3.42, 3.69, 3.82, and 3.92 l.min-1; HR = 93, 175, 181, 185, 189, and 194 beats.min-1; VE = 31, 99, 120, 129, 145, and 156 l.min-1; HLa = 2.9, 5.6, 7.2, 9.2, 10.6, and 13.5 mM). In six subjects (speed skaters), the peak values observed during time trial for HR (188 +/- 6 vs 191 +/- 5 beats.min-1) and HLa (16.4 +/- 3.1 vs 17.0 +/- 4.2 mM) were not significantly different than observed during real world competition.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Electromyographic analysis of four popular abdominal exercises.

This study was designed to evaluate the effects of four specific sit-up exercises on muscular activity of the rectus abdominis. Pairs of surface electrodes were placed unilaterally on four quadrants of the rectus abdominis, delimited by tendinous inscriptions, in four male subjects. Electromyographic (EMG) recordings were taken while the subjects performed four different abdominal exercises. Each abdominal exercise was hypothesized to have a specific effect on one of the four quadrants of the rectus abdominis. The four exercises analyzed were: 1) long lying crunch, 2) bent knee crunch, 3) leg raise, and 4) vertical leg crunch. Analysis of the standardized EMG recordings demonstrated no significant differences in the mean muscle activity between the four different quadrants, in the mean muscle activity between the four different exercises, and in interactions between the exercises and the quadrants of the rectus abdominis. We conclude that none of the four abdominal exercises studied are specific for strengthening individual muscle quadrants of the rectus abdominis.

Journal Article↗
PubMed1993

Effect of pacing strategy on cycle time trial performance.

Despite interest in competitive strategy by coaches and athletes, there are no systematically collected data regarding the effect of differences in pacing strategy on the outcome of middle distance (2-4 min duration) events. In this study different pacing strategies were evaluated using a 2-km time trial on a bicycle attached to a wind load simulator. Well-trained subjects (N = 9) performed five separate time trials with the pace during the first 50% of the trial experimentally constrained within the usual real world range from very slow (approximately 55% of best time) to very fast (approximately 48% of best time). Serial VO2 was measured to estimate the oxidative contributions to the trial and accumulated O2 deficit and postexercise blood lactate measured to estimate the anaerobic contribution to the trial. The evenly paced trial (first 1 km = 50.9% final time) produced the fastest total time. The starting pace to final time relationship was described by a U shaped second order polynomial curve with the nadir for final time at a starting pace of 51% of best total time. There were no systematic differences in serial VO2, accumulated O2 deficit, or postexercise lactate that could account for the pacing related variations in performance. The data support the concept of relatively even pacing in middle distance events with negative consequences for even small variations in this strategy.

Analysis of Variance↗