Differences In Endurance Performance Research Articles

Study on the Difference of Endurance Performance between Polarization Intensity and other Intensity Distribution Endurance Training

The purpose of this study is to explore the difference in the effect of endurance training with different intensity distribution on improving athletes ' endurance performance. Through systematic review and empirical analysis, the effects of polarization intensity training and other intensity distribution training in endurance exercise were compared. In this study, literature review, experimental design and data analysis were used to elaborate the theoretical basis, implementation strategy and influence mechanism of polarization intensity training on endurance performance. At the same time, other intensity distribution trainings were classified and described, and the potential effects of these training methods on endurance improvement were analyzed. Further, this study revealed the significant differences in endurance performance between the two training modes through comparative analysis, and discussed possible physiological explanations. Finally, this study puts forward training suggestions for different sports groups, and puts forward the prospect of future research direction. The results of this study show that polarization intensity training has obvious advantages in improving the performance of professional endurance athletes, but other intensity distribution training also shows good applicability and effect among amateur sports enthusiasts.

Determining V̇O2max in competitive swimmers: Comparing the validity and reliability of cycling, arm cranking, ergometer swimming, and tethered swimming

ObjectivesThis study aims to identify the optimal method for determining V̇O2max in competitive swimmers in terms of validity and test–retest reliability. DesignControlled experiment. MethodsTwenty competitive swimmers performed four maximal incremental exercise tests: cycling, arm cranking, ergometer swimming, and tethered swimming. Gas analysis was conducted to estimate V̇O2max. Validity was assessed in terms of the amount of variance of the performance on a 1500-m time trial explained by the estimated V̇O2max . Test–retest reliability was evaluated using the intraclass correlation coefficient (ICC). ResultsV̇O2max obtained from tethered swimming, ergometer swimming, and cycling explained a similar amount of variance of the 1500-m performance (R2 = 0.64, 0.64 and 0.65, respectively). However, ergometer swimming yielded significantly lower V̇O2max estimates (40.54 ± 6.55 ml/kg/min) than tethered swimming (54.40 ± 6.21 ml/kg/min) and cycling (54.39 ± 5.63 ml/kg/min). Arm cranking resulted in both a lower explained variance (R2 = 0.41) and a significantly lower V̇O2max (43.14 ± 7.81 ml/kg/min). Tethered swimming showed good reliability (ICC = 0.81). ConclusionsBicycle and tethered swimming tests demonstrated high validity with comparable V̇O2max estimates, explaining a large proportion of differences in endurance performance. Choosing between these two methods involves a trade-off between a higher practical applicability and reliability of the bicycle test and the more sport-specific nature of the tethered swimming test.

Physiological and biochemical in vivo study of polyphenols and 20-hydroxyecdisone from quinoa grains effect on resistance to physical exercise in Wistar rats

Increasing the ability of the human body to adapt to physical stress is relevant from the standpoint of using foods for special uses containing functional food ingredients (FFI) with effectiveness proven in vivo. The purpose of this study was to evaluate the effect of FFI from Chenopodium quinoa grains with a high content of polyphenols and phytoecdysteroids on the physical endurance of male Wistar rats. Material and methods. The experiment was carried out during 36 days using 50 weaned male Wistar rats. The animals were randomly divided into 3 groups (n=12): Control, Run and Run-FFI. Rats of the Control and Run groups received a standard semisynthetic diet during the experiment. Rats of the Run-FFI group received a semi-synthetic diet with the addition of FFI in an amount of 0.055±0.003%, containing phytoecdysteroids (50.4±0.6 mg/g) and polyphenols (212.0±2.0 mg/g). During the experiment, the rats were assessed for their neuromotor function (grip strength of front paws), memory, and behavioral reactions in the "Elevated Plus Maze" (EPM), "Conditioned Passive Avoidance Reflex" (CPAR) and "Open Field" (OF) tests. Once a week, animals from the Run and Run-FFI groups were subjected to moderate physical load on a "Treadmill". On the 36th day of the experiment, the animals of these groups were subjected to exhausting physical load. Immediately after running, the animals were placed in metabolic cages to collect daily urine. At the end of the experiment, the content of corticosterone, the activity of catalase, indicators of protein, lipid and mineral metabolism, indexes of the liver functional state and antioxidant defense system parameters were analyzed in the blood serum; the level of prostaglandin E2 and dopamine were determined in daily urine. Results. Physiological tests (CRAR, OF) showed that weekly exercise increased anxiety in laboratory animals. The FFI introduction into the diet led to normalization of the assessed parameters (EPM). As a result of 36-day consumption of FFI against the background of physical loads, a significant decrease by 22% in the main stress marker, corticosterone, was revealed in the blood of rats, as well as significant increase by 23% in the stress inhibitor - prostaglandin E2 urinary excretion, compared with animals of the Run group to the level not differed from the indicators of the control animals. There were no differences in endurance performance between the Run and Run-FFI groups on the results of the exhaustive exercise. Consumption of FFI prevented the formation of excess ammonia, significantly reducing the level of urea in the blood and normalizing its excretion to control levels in the urine, which was increased in the Run group by 19%. Conclusion. The results obtained demonstrated the adaptogenic properties of the developed FFI in response to stress caused by weekly moderate and acute exhaustive physical activity. The obtained data on the biological effect of the developed FPI on the adaptive potential of laboratory animals will serve as an experimental basis for its inclusion in the composition of specialized foods.

ENDURANCE PERFORMANCE IN BASKETBALL: COMPARISON BY AGE CATEGORIES

The aim of this study was to investigate the endurance performance in the male basketball players according to age categories. Totally 89 male healthy basketball players (age between 10-16 years) were voluntarily participated in this study. The age categories are determined as under 12 age (U12) novice, under 14 age (U14) little, under 16 age (U16) youth and under 18 age (U18) junior. 20 m shuttle-run test applied to determine the endurance performances of the subjects. VO2max, number of laps and total distance parameters are examined. It has been found that endurance performance increases with age. However, this increase was determined to be significantly different between the age categories (p<0.05). Although it was determined that endurance performance increased with age in male basketball athletes, there is no significant difference in endurance performance between U12 and U14. It is recommended to examine the lack of difference between novice and little teams in terms of adolescence and/or transition to adolescence.

Endurance Trained Athletes Do Not per se Have Higher Hoffmann Reflexes Than Recreationally Active Controls

The impact of endurance training on spinal neural circuitries remains largely unknown. Some studies have reported higher H-reflexes in endurance trained athletes and therefore, adaptations within the Ia afferent pathways after long term endurance training have been suggested. In the present study we tested the hypothesis that cyclists (n = 12) demonstrate higher Hoffmann reflexes (H-reflexes) compared to recreationally active controls (n = 10). Notwithstanding, highly significant differences in endurance performance (VO2peak: 60.6 for cyclists vs. 46.3 ml/min/kg for controls (p < 0.001) there was no difference in the size of the SOL H-reflex between cyclists and controls (Hmax/Mmax ratio 61.3 vs. 60.0%, respectively (p = 0.840). Further analyses of the H and M recruitment curves for SOL revealed a significant steeper slope of the M recruitment curve in the group of cyclists (76.2 ± 3.8° vs. 72.0 ± 4.4°, p = 0.046) without a difference in the H-recruitment curve (84.6 ± 3.0° vs. 85.0 ± 2.8°, p = 0.784) compared to the control group. Cycling is classified as an endurance sport and thus the findings of the present study do not further support the assumption that long-term aerobic training leads to a general increase of the H-reflex. Amongst methodological differences in assessing the H-reflex, the training-specific sensorimotor control of the endurance sport itself might differently affect the responsiveness of spinal motoneurons on Ia-afferent inputs.

Using Accelerometry for Evaluating Energy Consumption and Running Intensity Distribution Throughout a Marathon According to Sex.

The proportion of females participating in long-distance races has been increasing in the last years. Although it is well-known that there are differences in how females and males face a marathon, higher research may be done to fully understand the intrinsic and extrinsic factors affecting sex differences in endurance performance. In this work, we used triaxial accelerometer devices to monitor 74 males and 14 females, aged 30 to 45 years, who finished the Valencia Marathon in 2016. Moreover, marathon split times were provided by organizers. Several physiological traits and training habits were collected from each participant. Then, we evaluated several accelerometry- and pace-estimated parameters (pacing, average change of speed, energy consumption, oxygen uptake, running intensity distribution and running economy) in female and male amateur runners. In general, our results showed that females maintained a more stable pacing and ran at less demanding intensity throughout the marathon, limiting the decay of running pace in the last part of the race. In fact, females ran at 4.5% faster pace than males in the last kilometers. Besides, their running economy was higher than males (consumed nearly 19% less relative energy per distance) in the last section of the marathon. Our results may reflect well-known sex differences in physiology (i.e., muscle strength, fat metabolism, VO2max), and in running strategy approach (i.e., females run at a more conservative intensity level in the first part of the marathon compared to males). The use of accelerometer devices allows coaches and scientific community to constantly monitor a runner throughout the marathon, as well as during training sessions.

Hypohydration And Endurance Performance: A Meta-analysis

PURPOSE: The primary purpose of this meta-analysis was to systematically evaluate the differences in endurance performance while in a hypohydrated state achieved through varying dehydration methods. A secondary purpose was to evaluate the moderation between types of hypohydration (fluid restricted vs. exercise-induced) and changes in heart rate and core temperature. METHODS: A systematic literature search of databases and specific journals relating to the subject, as well as a forward search with relevant researchers was performed to identify research papers meeting the inclusion criteria. RESULTS: Eleven total studies met the inclusion criteria including a minimum of 2% hypohydration. All 11 included articles measured heart rate and 6 included articles measured core temperature. The meta-analysis using a random effects model indicated a hypohydration had a significant impact of hydration on heart rate (ES = -0.42, p <.00) and core temperature (ES = - 0.6, p = .017). Method of dehydration did not significantly moderate the change in heart rate (p = .59) or core temperature (p = .37). CONCLUSIONS: Heart rate and core temperature are elevated in a hypohydrated state. Current literature does not suggest that the method of dehydration impacts the elevation of heart rate and core temperature.

Differing Physiological Adaptations Induced by Dry and Humid Short-Term Heat Acclimation.

To investigate the effect of a 5-day short-term heat acclimation (STHA) protocol in dry (43°C and 20% relative humidity) or humid (32°C and 80% relative humidity) environmental conditions on endurance cycling performance in temperate conditions (21°C). In a randomized, cross-over design, 11 cyclists completed each of the two 5-day blocks of STHA matched for heat index (44°C) and total exposure time (480min), separated by 30 days. Pre- and post-STHA temperate endurance performance (4-min mean maximal power, lactate threshold 1 and 2) was assessed; in addition, a heat stress test was used to assess individual levels of heat adaptation. Differences in endurance performance were unclear. Following dry STHA, gross mechanical efficiency was likely reduced (between-condition effect size dry vs humid -0.59; 90% confidence interval, -1.05 to -0.15), oxygen uptake was likely increased for a given workload (0.64 [0.14 to 1.07]), and energy expenditure likely increased (0.59 [0.17 to 1.03]). Plasma volume expansion at day 5 of acclimation was similar (within-condition outcome 4.6% [6.3%] and 5.3% [5.1%] dry and humid, respectively) but was retained for 3 to 4 days longer after the final humid STHA exposure (-0.2% [8.1%] and 4.5% [4.2%] dry and humid, respectively). Sweat rate was very likely increased during dry STHA (0.57 [0.25 to 0.89]) and possibly increased (0.18 [-0.15 to 0.50]) during humid STHA. STHA induced divergent adaptations between dry and humid conditions, but did not result in differences in temperate endurance performance.

Effect of Sequencing Strength and Endurance Training in Young Male Soccer Players.

This study examined the effects of strength and endurance training sequence (strength before or after endurance) on relevant fitness variables in youth soccer players. Fifty-seven young elite-level male field soccer players (13.7 ± 0.5 years; 164 ± 8.3 cm; 53.5 ± 8.6 kg; body fat; 15.6 ± 3.9%) were randomly assigned to a control (n = 14, CG) and 3 experimental training groups (twice a week for 12 weeks) strength before (SE, n = 15), after (ES, n = 14) or on alternate days (ASE, n = 14) with endurance training. A significant (p = 0.001) intervention main effect was detected. There were only trivial training sequence differences (ES vs. SE) for all variables (p > 0.05). The CG showed large squat 1 repetition maximum (1RM) and medium sprint, change of direction ability, and jump improvements. ASE demonstrated a trivial difference in endurance performance with ES and SE (p > 0.05). Large to medium greater improvements for SE and ES were reported compared with ASE for sprinting over 10 and 30 m (p < 0.02). The SE squat 1RM was higher than in ASE (moderate, p < 0.02). Postintervention differences between ES and SE with CG fitness variables were small to medium (p ≤ 0.05) except for a large SE advantage with the Yo-Yo intermittent recovery test (p < 0.001, large). This study showed no effect of intrasession training sequence on soccer fitness-relevant variables. However, combining strength and endurance within a single training session provided superior results vs. training on alternate days. Concurrent training may be considered as an effective and safe training method for the development of the prospective soccer player.

Gender differences in endurance performance by elite cross‐country skiers are influenced by the contribution from poling

Greater gender differences have been found in exercise modes where the upper body is involved. Therefore, the present study investigated the influence of poling on gender differences in endurance performance by elite cross-country skiers. Initially, the performance of eight male and eight female sprint skiers was compared during four different types of exercise involving different degrees of poling: double poling (DP), G3 skating, and diagonal stride (DIA) techniques during treadmill roller skiing, and treadmill running (RUN). Thereafter, DP was examined for physiological and kinematic parameters. The relative gender differences associated with the DP, G3, DIA and RUN performances were approximately 20%, 17%, 14%, and 12%, respectively. Thus, the type of exercise exerted an overall effect on the relative gender differences (P < 0.05). In connection with DP, the men achieved 63%, 16%, and 8% higher VO2peak than the women in absolute terms and with normalization for total and fat-free body mass (all P < 0.05). The DP VO2peak in percentage of VO2max in RUN was higher in men (P < 0.05). The gender difference in DP peak cycle length was 23% (P < 0.05). In conclusion, the present investigation demonstrates that the gender difference in performance by elite sprint skiers is enhanced when the contribution from poling increases.

Sun-Dried Raisins are a Cost-Effective Alternative to Sports Jelly Beans in Prolonged Cycling

The purpose of this study was to examine the effects of a natural carbohydrate (CHO) source in the form of sun-dried raisins (SDRs) vs. Sports Jelly Beans™ (SJBs) on endurance performance in trained cyclists and triathletes. Ten healthy men (18-33 years) completed 1 water-only acclimatization exercise trial and 2 randomized exercise trials administered in a crossover fashion. Each trial consisted of a 120-minute constant-intensity glycogen depletion period followed by a 10-km time trial (TT). During each experimental trial, participants consumed isocaloric amounts of SDRs or SJBs in 20-minute intervals. Measurements included time to complete 10-km TT, power output during 10-km TT, blood glucose levels and respiratory exchange ratio during glycogen depletion period, rate of perceived exertion (RPE), 'flow' questionnaire responses, and a hedonic (i.e., pleasantness) sensory acceptance test. There were no significant differences in endurance performance for TT time (SDRs vs. SJBs, 17.3 ± 0.4 vs. 17.3 ± 0.4 seconds) or power (229.3 ± 13.0 vs. 232.0 ± 13.6 W), resting blood glucose levels (5.8 ± 04 mmol·L(-1) for SDRs and 5.4 ± 0.2 mmol·L(-1) for SJBs), RPE, or flow experiences between SDR and SJB trials. However, the mean sensory acceptance scores were significantly higher for the SDRs compared to the SJBs (50.7 ± 1.7 vs. 44.3 ± 2.7). Consuming SDRs or SJBs during 120 minutes of intense cycling results in similar subsequent TT performances and are equally effective in maintaining blood glucose levels during exercise. Therefore, SDRs are a natural, pleasant, cost-effective CHO alternative to commercial SJBs that can be used during moderate- to high-intensity endurance exercise.

Oxygen Uptake, Velocity at Lactate Threshold, and Running Economy in Elite Special Forces

To examine the correlation of peak oxygen uptake (VO2 peak), velocity at lactate threshold (V(LT)), and running economy (RE) in a group of Special Force Squad members. VO2 peak, V(LT), and RE of 120 male elite special force police squad members (VO2 peak, 57.4 +/- 4.3 mL minute(-1) kg(-1); age, 28.9 +/- 5.2 years; body mass index, 24.2 +/- 1.6 kg m(-2)) were tested using an incremental treadmill protocol (2.4 m second(-1), increase 0.4 m second(-1) every 5 minutes). Running velocities at the first lactate inflection point (V(LT)) and blood lactate concentration at 4 mmol L(-1) (V4) were determined. RE was defined as oxygen uptake in mL kg(-1) minute(-1) at 3.2 m second(-1). Analysis revealed little or no correlation between V4, V(LT), VO2 peak, and RE (r = 0.02-0.35; p = 0.01-0.80). (1) VO2 peak, V(LT), and RE do not correlate in elite squad members. (2) All 3 variables should be assessed when comparing inter- and intraindividual differences in endurance performance of Special Force Squad members.

The effects of increased absolute training intensity on adaptations to endurance exercise training

“Progressive overload” is regarded an important principle to consider in maximising endurance training adaptations, yet little scientific evidence supports this concept. The aim of the present study was to compare differences in endurance performance after a training regime where treadmill-running intensity was incrementally elevated to a regime where running intensity remained unchanged. Twenty-eight healthy untrained males and females were randomly and equally assigned into both regimes. All participants performed 20 min treadmill-running sessions 3 times a week for 6 weeks. Prior to and after training, maximum oxygen uptake ( V ˙ O 2max ), oxygen uptake and velocity at the lactate threshold (LTVO 2 and LTv) and maximum treadmill velocity ( V max) were measured in an incremental treadmill test. 5000 m time trial performance was also assessed. In the incremental intensity regime treadmill velocity commenced at 0.8 km·h −1 below the LTv and was increased by 0.1 km·h −1 every session. In the constant intensity regime treadmill speed was kept constant at 0.8 km·h −1 below the LTv for the duration of the training. The study revealed that both regimens increased V ˙ O 2max , V max LTVO 2, LTv and decreased 5000 m time trial significantly after training. There were no significant differences in the changes between regimens for V ˙ O 2max , V max and 5000 m time trial. However, the increase in LTVO 2 and LTv were significantly greater in the incremental intensity regime compared to the constant intensity regime. The present data show that 20 min treadmill-running sessions performed 3 times a week for 6 weeks improves endurance performance and that progressively elevating exercise intensity is important to maximise improvements in LTVO 2 and LTv.

Is peripheral locomotor muscle fatigue during endurance exercise a variable carefully regulated by a negative feedback system?

Is peripheral locomotor muscle fatigue during endurance exercise a variable carefully regulated by a negative feedback system?

Oral Contraceptive Phase Has no Effect on Endurance Test

Thirteen female cyclists/triathletes (mean peak VO(2) = 53.0 + 5.6 ml . kg (-1) . min (-1)) using a monophasic oral contraceptive (OC) performed an endurance test (1-h cycle) at three time points of an OC cycle. Testing times were during the OC consumption phase (CONS), early in the OC withdrawal phase (WITH1) and late in the OC withdrawal phase (WITH2). Resting endogenous serum oestradiol and progesterone concentrations were measured. Power output, heart rate (HR), ventilation (V(E)), oxygen consumption (VO(2)), respiratory exchange ratio (RER), rating of perceived exertion (RPE), blood lactate and blood glucose were measured throughout the 1-h test. Serum oestradiol levels were greater during WITH2 compared to the CONS (p < 0.05). No significant differences were present between the testing times for mean power output (172 - 173 watts), HR (163 - 166 bpm), VO(2) (41.3 - 41.7 mL . kg (-1) . min (-1)), RER (0.93 - 0.94), RPE (14.5 - 14.8) and blood glucose concentration (5.3 - 5.5 mmol . L (-1)) (p > 0.05). Greater mean V. (E) (by 3.4 and 5.7 L . min (-1)) and VE/VO(2) (by 1.0 and 2.0) values were measured during CONS compared to WITH1 and WITH2 respectively and blood lactate values (by 1.2 mmol . L (-1)) compared to WITH1 only (p < 0.05). Despite variation in some physiological variables, there was no difference in endurance performance throughout an OC cycle in endurance trained female athletes.

Coingestion of Carbohydrate-Protein during Endurance Exercise: Influence on Performance and Recovery

Endurance athletes commonly consume carbohydrate-electrolyte sports beverages during prolonged events. The benefits of this strategy are numerous--sports-beverage consumption during exercise can delay dehydration, maintain blood glucose levels, and potentially attenuate muscle glycogen depletion and central fatigue. Thus, it is generally agreed that carbohydrate-electrolyte beverages can improve endurance performance. A controversy has recently emerged regarding the potential role of protein in sports beverages. At least 3 recent studies have reported that carbohydrate-protein ingestion improves endurance performance to a greater extent than carbohydrate alone. In addition, carbohydrate-protein ingestion has been associated with reductions in markers of muscle damage and improved postexercise recovery.Although many of these muscle damage and recovery studies examined postexercise nutritional intake, recent evidence suggests that these benefits may be elicited with carbohydrate-protein consumption during exercise. These findings are intriguing and suggest that the importance of protein for endurance athletes has been underappreciated. However, 2 studies recently reported no differences in endurance performance between carbohydrate and carbohydrate-protein beverages. The varied outcomes may have been influenced by a number of methodological differences, including the amounts and types of carbohydrate or protein in the beverages, the exercise protocols, and the relative statistical power of the studies. In addition, although there are plausible mechanisms that could explain the ergogenic effects of carbohydrate-protein beverages, they remain relatively untested. This review examines the existing research regarding the efficacy of carbohydrate-protein consumption during endurance exercise. Limitations of the existing research are addressed, as well as potential areas for future study.

Trunk muscle endurance tests: Reliability, and comparison of holding times between male and female athletes

Adequate trunk muscle endurance may play an important role in injury-free performance amongst athletes. However, reliability of tests of isometric trunk muscle endurance in common use has not been clearly established and few studies have reported normative data for athletes. Work to date has tended to focus on trunk flexor and extensor endurance, with less attention to the lateral trunk muscles. This study first examined intra-rater and inter-rater reliability of the side bridge endurance test and a test of trunk flexor endurance in a group of non-athletes, then measured performance of a group of elite athletes on tests of trunk muscle endurance commonly used in the clinic. The side bridge endurance test and the trunk flexor endurance test were found to have high intra-rater and inter-rater reliability, albeit with relatively large standard error of measurement (S.E.M.) values. In contrast with previous studies of non-athletes, male athletes had holding times on the Biering—Sorensen trunk extensor endurance test that were equivalent to those of female athletes. However, female athletes had significantly shorter holding times on both the left and right side bridge endurance tests than their male counterparts. The implication of the significant difference in endurance performance between male and female athletes in some muscle groups but not others is that testing and training of trunk muscle endurance should be ‘multidirectional’ for all athletes who aim to optimise their performance and minimise their injury risk.

Trunk muscle endurance tests: Reliability, and gender differences in athletes

Adequate trunk muscle endurance may play an important role in injury-free performance among athletes. However, reliability of tests of isometric trunk muscle endurance in common use has not been clearly established and few studies have reported normative data for athletes. This study first examined intra-rater and inter-rater reliability of the side bridge endurance test and a test of trunk flexor endurance in a group of non-athletes, then measured performance of a group of elite athletes on tests of trunk muscle endurance commonly used in the clinic. The side bridge endurance test and the trunk flexor endurance test were found to have high intra-rater and inter-rater reliability, albeit with relatively large standard error of measurement (S.E.M.) values. In contrast with previous studies of non-athletes, male athletes had equivalent holding times on the Biering-Sørensen trunk extensor endurance test to those of female athletes. However, female athletes had significantly lower holding times on the side bridge endurance tests than their male counterparts. The implication of the significant difference in endurance performance between male and female athletes in some muscle groups but not others is that testing and training of trunk muscle endurance should be 'multidirectional' for all athletes who aim to optimise performance and minimise injury risk.

Gender differences in skeletal muscle fatigability are related to contraction type and EMG spectral compression.

The purposes of this study were 1) to evaluate gender differences in back extensor endurance capacity during isometric and isotonic muscular contractions, 2) to determine the relation between absolute load and endurance time, and 3) to compare men [n = 10, age 22.4 +/- 0.69 (SE) yr] and women (n = 10, age 21.7 +/- 1.07 yr) in terms of neuromuscular activation patterns and median frequency (MF) shifts in the electromyogram (EMG) power spectrum of the lumbar and hip extensor muscles during fatiguing submaximal isometric trunk extension exercise. Subjects performed isotonic and isometric trunk extension exercise to muscular failure at 50% of maximum voluntary contraction force. Women exhibited a longer endurance time than men during the isometric task (146.0 +/- 10.9 vs. 105.4 +/- 7.9 s), but there was no difference in endurance performance during the isotonic exercise (24.3 +/- 3.4 vs. 24.0 +/- 2.8 repetitions). Absolute load was significantly related to isometric endurance time in the pooled sample (R(2) = 0.34) but not when men and women were analyzed separately (R(2) = 0.05 and 0.04, respectively). EMG data showed no differences in neuromuscular activation patterns; however, gender differences in MF shifts were observed. Women demonstrated a similar fatigability in the biceps femoris and lumbar extensors, whereas in men, the fatigability was more pronounced in the lumbar musculature than in the biceps femoris. Additionally, the MF of the lumbar extensors demonstrated a greater association with endurance time in men than in women (R(2) = 0.45 vs. 0.19). These findings suggest that gender differences in muscle fatigue are influenced by muscle contraction type and frequency shifts in the EMG signal but not by alterations in the synergistic activation patterns.

EFFECT OF BLOOD VOLUME EXPANSION ON ??VO2MAX, ENDURANCE PERFORMANCE AND CARDIAC FUNCTION IN ENDURANCE ATHLETES 806

Recent work in our laboratory suggests that the greater portion of the enhancement in cardiac function seen in endurance-trained athletes is simply a passive response to their higher blood volume (BV). We speculated that an additional increase in plasma volume (PVexp), (500 ml of 6% dextran) would lead to further enhancements in their endurance performance, ˙VO2 max and cardiac function. Therefore, nine highly trained endurance cyclists(˙VO2 max ≥ 65 ml·kg-1·min-1) were studied employing a double blind, cross-over design; i) before PVexp(Ctrl 1), ii) following sham PVexp (Sham), iii) following restoration to normocythemia (Ctrl 2), iv) after PVexp, andv) upon re-establishment of control haematologic levels (Ctrl 3). PVexp resulted in a 547 ± 61 ml increase in BV (p < 0.05). The consequent hemodilution resulted in a reduction of 6% in both the oxygen-carrying capacity and oxygen content of blood. There were no significant differences in endurance performance or ˙VO2 max among conditions. Following PVexp, left ventricular ejection time was significantly increased but there were no significant changes in left ventricular ejection rate, diastolic filling time or diastolic filling rate. As well, PVexp had no significant effect on arterial blood pressure or total peripheral resistance. Maximal cardiac output (Qmax) and maximal stroke volume (SVmax) were significantly higher following PVexp (3.2% and 3.4% respectively), which was sufficient to offset the hemodilution effects of PVexp and allow˙VO2 max and endurance performance to remain unchanged. These results suggest that in endurance-trained athletes who already have a high BV, an additional increase in PV will not result in a sufficient increase in SVmax and Qmax to overcome the hemodilution effects of acute Pvexp, resulting in no further enhancements in endurance performance, ˙VO2 max or cardiac function. Thus, endurance athletes may be at an optimal BV which is at the limits of their diastolic reserve capacity.