Changes In Endurance Capacity Research Articles

Inhibition of Oxidative Stress by Antioxidant Supplementation Does Not Limit Muscle Mitochondrial Biogenesis or Endurance Capacity in Rats.

The objective of the present study was to analyze the activation and expression patterns of upstream and downstream factors of PGC-1α to determine whether antioxidant (AO) supplementation inhibits mitochondrial biogenesis in skeletal muscles as an adaptation to endurance training, as well as to analyze changes in endurance capacity based on such findings. For this objective, 24 male Sprague-Dawley (SD) rats were allocated into 4 groups (vehicle-sedentary, V-Sed; vehicle-exercise, V-EX; antioxidant-sedentary, AO-Sed; antioxidant-exercise, AO-EX) of 6 rats each. The rats were then treated with vitamin C (500 mgkg-1 body weightd-1) or a placebo for 8 wk, and a swimming program was implemented in some rats during the last 4 wk of this period. Immediately after the last training session, blood was collected from the tail of each rat, and TBARS was measured to test the effect of vitamin C as an AO. As a result, increased oxidative stress from exercise was inhibited by vitamin C supplementation. Analysis of whether reduced oxidative stress by vitamin C supplementation also inhibited mitochondrial biogenesis within skeletal muscles showed that phosphorylation of p38 MAPK and AMPK, along with levels of PGC-1α, NRF-1, mtTFA, and mitochondrial electron transport enzymes, increased after endurance training in spite of vitamin C supplementation. Moreover, running time, distance, and total work increased significantly in the exercise group as compared to those in the sedentary group, regardless of vitamin C supplementation. These results indicate that mitochondrial biogenesis and endurance capacity increase as a result of endurance training, regardless of AO supplementation.

Strength Training Increases Endurance Time to Exhaustion During High-Intensity Exercise Despite No Change in Critical Power

The purpose of this study was to determine whether improvements in endurance exercise performance elicited by strength training were accurately reflected by changes in parameters of the power-duration hyperbola for high-intensity exercise. Before and after 8 weeks of strength training (N = 14) or no exercise, control (N = 5), 19 males (age: 20.6 ± 2.0 years; weight: 78.2 ± 15.9 kg) performed a maximal incremental exercise test on a cycle ergometer and also cycled to exhaustion during 4 constant-power exercise bouts. Critical power (CP) and anaerobic work capacity (W') were estimated using nonlinear and linear models. Subjects in the strength training group improved significantly more than controls (p < 0.05) for strength (~30%), power at V[Combining Dot Above]O2peak (7.9%), and time to exhaustion (TTE) for all 4 constant-power tests (~39%). Contrary to our hypothesis, CP did not change significantly after strength training (p > 0.05 for all models). Strength training improved W' (mean range of improvement = +5.8 to +10.0 kJ; p < 0.05) for both linear models. Increases in W' were consistently positively correlated with improvements in TTE, whereas changes in CP were not. Our findings indicate that strength training alters the power-duration hyperbola such that W' is enhanced without any improvement in CP. Consequently, CP may not be robust enough to track changes in endurance capacity elicited by strength training, and we do not recommend it to be used for this purpose. Conversely, W' may be the better indicator of improvement in endurance performance elicited by strength training.

A Submaximal Test for the Assessment of Knee Extensor Endurance Capacity

We aimed to develop an undemanding test for endurance capacity of the knee extensor muscles, which can also be applied to frail participants. We hypothesized 1) that the first objective indications for peripheral fatigue during incremental unilateral repetitive isometric knee extensor contractions could be used to assess a fatigue threshold (FT), 2) that torque at FT would depend on training status, and 3) that this torque could easily be sustained for 30 min. Five trained and five untrained participants performed 5-min bouts of 60 repetitive contractions (3-s on and 2-s off). Torque, set at 25% maximal voluntary contraction (MVC), was increased by 5% MVC in subsequent bouts. The highest torque for which rectified surface EMG remained stable during the bout was defined as the FT. On separate occasions, 30-min bouts were performed at and above the FT to assess sustainable torque. Changes in gas exchange parameters, HR, and RPE were monitored to corroborate FT. At FT (RPE = 5.7 ± 1.7), torque was higher (P < 0.05) in trained (41.4% ± 5.8% MVC) than in untrained participants (30.5% ± 1.8% MVC). Sustainable torque was ∼4% higher than (P < 0.05) and significantly related to FT (r(2) = 0.79). When torque was increased by 5% MVC, significant increases in rectified surface EMG and V˙O2 were found. During incremental knee extensor contractions, FT could be assessed at a submaximal exercise intensity. FT was higher in trained than in untrained participants and was related to exercise sustainability. With the use of FT, changes in endurance capacity of single muscle groups can potentially also be determined in frail participants for whom exercise performed until exhaustion is unwarranted.

Knee Extensor Fatigue Threshold Is Related to Whole-Body V˙O2max

Above a given exercise intensity, rapid muscle fatigue will occur. We explored the possibility of assessing torque threshold for peripheral fatigue during single-legged repetitive isometric knee extensor exercise. We hypothesized this fatigue threshold to be related to the general aerobic fitness level and the so-called "critical torque" (CT) established with a recently validated 5-min all-out test. Seventeen healthy men (VO(2max) = 44.7-69.6 mL·kg(-1)·min(-1)) performed six submaximal (20%-55% maximal voluntary contraction [MVC]) 5-min bouts of 60 repetitive contractions (3-s on, 2-s off). Torque was changed between bouts in steps of 5% MVC to estimate the highest intensity (fatigue threshold) at which average changes in rsEMG, EMG median power frequency, and tissue deoxygenation (near-infrared spectroscopy) of the three superficial knee extensor muscles were still <5%, signifying steady-state exercise with minimal peripheral fatigue. On another occasion, one bout was performed in an all-out manner with end-test torque representing CT. Fatigue threshold (40.0% ± 8.1% MVC) was related (r(2) = 0.57, P < 0.05) to CT (53.1% ± 10.0% MVC), but it was consistently lower (P < 0.05) and only fatigue threshold was significantly related to VO(2max) (r(2) = 0.68), and the first (r(2) = 0.45) and second (r(2) = 0.63) ventilatory threshold obtained during cycle ergometry. Performing submaximal bouts of knee extensor contractions, while monitoring EMG and deoxygenation, seems a feasible manner to estimate an aerobic capacity-related exercise intensity of peripheral fatigue onset. This test may be used to evaluate changes in endurance capacity of single muscle groups, without the necessity for all-out testing, which could be problematic with frail subjects.

Time Course of Changes in Endurance Capacity

To investigate the magnitude and the time course of changes in endurance capacity during the first year of an aerobic endurance training program with constant HR prescription. Eighteen previously untrained subjects (7 males and 11 females, 42 +/- 5 yr, BMI of 24.3 +/- 2.5 kg x m(-2), and maximal oxygen uptake (VO(2max)) of 37.7 +/- 4.6 mL x min(-1) x kg(-1)) completed a 12-month jogging/walking program on 3 d x wk(-1) 45 min per session with a constant HR prescription of 60% HR reserve. Exhaustive treadmill tests were conducted before the intervention and after 3, 6, 9, and 12 months of training. In addition, submaximal tests on an indoor running track were performed every 4 wk. After 12 months, VO(2max) had increased by 0.36 +/- 0.33 L x min(-1) (median [interquartile range]: 16% [9%-20%], P < 0.001). After 3, 6, and 9 months, 52%, 65%, and 79% of this increase were reached, respectively. Resting HR decreased by a total of 9 +/- 6 min(-1) (P<0.001). Of this change, 47% and 102% had occurred after 3 and 6 months, respectively. Submaximal exercise HR during the treadmill tests decreased by 11 +/- 7 min(-1) (P < 0.001) on average. After 3 and 6 months of training, 93% and 101% of this change were observed, respectively. The running track tests revealed that submaximal exercise HR did not change significantly after the ninth week of training. Beginners in recreational endurance exercise are advised to increase their training stimulus after 6 months of training to maintain training effectiveness because no further significant changes in endurance capacity were observed thereafter. When planning future endurance training studies in untrained subjects, it should be taken into account that submaximal exercise HR might reflect endurance changes during the first week only, whereas VO(2max) remains responsive after several months.

Lactate Threshold Concepts

During the last nearly 50 years, the blood lactate curve and lactate thresholds (LTs) have become important in the diagnosis of endurance performance. An intense and ongoing debate emerged, which was mainly based on terminology and/or the physiological background of LT concepts. The present review aims at evaluating LTs with regard to their validity in assessing endurance capacity. Additionally, LT concepts shall be integrated within the 'aerobic-anaerobic transition' - a framework which has often been used for performance diagnosis and intensity prescriptions in endurance sports. Usually, graded incremental exercise tests, eliciting an exponential rise in blood lactate concentrations (bLa), are used to arrive at lactate curves. A shift of such lactate curves indicates changes in endurance capacity. This very global approach, however, is hindered by several factors that may influence overall lactate levels. In addition, the exclusive use of the entire curve leads to some uncertainty as to the magnitude of endurance gains, which cannot be precisely estimated. This deficiency might be eliminated by the use of LTs. The aerobic-anaerobic transition may serve as a basis for individually assessing endurance performance as well as for prescribing intensities in endurance training. Additionally, several LT approaches may be integrated in this framework. This model consists of two typical breakpoints that are passed during incremental exercise: the intensity at which bLa begin to rise above baseline levels and the highest intensity at which lactate production and elimination are in equilibrium (maximal lactate steady state [MLSS]). Within this review, LTs are considered valid performance indicators when there are strong linear correlations with (simulated) endurance performance. In addition, a close relationship between LT and MLSS indicates validity regarding the prescription of training intensities. A total of 25 different LT concepts were located. All concepts were divided into three categories. Several authors use fixed bLa during incremental exercise to assess endurance performance (category 1). Other LT concepts aim at detecting the first rise in bLa above baseline levels (category 2). The third category consists of threshold concepts that aim at detecting either the MLSS or a rapid/distinct change in the inclination of the blood lactate curve (category 3). Thirty-two studies evaluated the relationship of LTs with performance in (partly simulated) endurance events. The overwhelming majority of those studies reported strong linear correlations, particularly for running events, suggesting a high percentage of common variance between LT and endurance performance. In addition, there is evidence that some LTs can estimate the MLSS. However, from a practical and statistical point of view it would be of interest to know the variability of individual differences between the respective threshold and the MLSS, which is rarely reported. Although there has been frequent and controversial debate on the LT phenomenon during the last three decades, many scientific studies have dealt with LT concepts, their value in assessing endurance performance or in prescribing exercise intensities in endurance training. The presented framework may help to clarify some aspects of the controversy and may give a rationale for performance diagnosis and training prescription in future research as well as in sports practice.

Influence Of Training Protocol On Endurance Effects

PURPOSE To determine the effect of deviating from commonly recommended training regimens on the size of changes in endurance capacity with regard to the weekly distribution of training sessions and the choice of exercise intensity. METHODS 51 healthy untrained subjects (44 ± 8 yrs, BMI 26.9 ± 5.3, VO2max 36.8 ± 8.6 ml*min−1*kg−1) were stratified for endurance capacity and sex and randomly assigned to 4 groups: regular training (REG, n=12, 5 sessions per week, 30 min each, intensity at 90% of the estimated maximal lactate steady state), “weekend warrior” (WW, n=13, 2 consecutive days per week for 75 min at the same intensity as REG), “fat burner” (FB, n=13, 5 sessions per week at a heart rate [HR] 15 min−1 below REG intensity), and control (CO, n=13, no training). Total energy output was held constant between the training groups which implied prolonging session durations for FB on an individual basis by 5 to 15 min to match the two other training groups. Training was conducted over 12 weeks and each session monitored by means of portable heart rate recorders. Identical graded treadmill protocols with simultaneous gas exchange, HR, and lactate measurements prior to and after the training program served for exercise prescription (given as HR ranges of 5–10 min−1) and documentation of endurance effects. RESULTS VO2max improved similarly and in all 3 training groups (REG +1.52 ml*min−1*kg−1, WW +3.37 ml*min−1*kg−1, FB +1.77 ml*min−1*kg−1). This effect was significant compared with CO (−0.95 ml*min−1*kg−1; p<0.05 for FB and REG; p<0.01 for WW). In comparison with CO (decrease by 3 min−1), average HR during incremental treadmill exercise decreased significantly by 9 min−1 (REG, p<0.05), 11 min−1 (WW, p<0.01), and 6 min−1 (FB, p<0.05). Only for the observed rightward shift of the lactate performance relationship, one group (FB) did not reach significant differences to CO. In absolute terms, the largest training gains were documented in WW. However, differences to the other training groups remained insignificant throughout. CONCLUSIONS In a middle-age population, deviations from commonly recommended weekly scheduling of training or from the choice of moderate intensity does not lead to major impairment of expectable improvements in endurance capacity provided the energy output is held equal. There are slight indications that the choice of a too low intensity might be more detrimental to positive training effects than piling up training sessions at the weekends as it is often practiced due to occupational constraints.

Influence Of Training Protocol On Endurance Effects

PURPOSE To determine the effect of deviating from commonly recommended training regimens on the size of changes in endurance capacity with regard to the weekly distribution of training sessions and the choice of exercise intensity. METHODS 51 healthy untrained subjects (44 ± 8 yrs, BMI 26.9 ± 5.3, VO2max 36.8 ± 8.6 ml*min−1*kg−1) were stratified for endurance capacity and sex and randomly assigned to 4 groups: regular training (REG, n=12, 5 sessions per week, 30 min each, intensity at 90% of the estimated maximal lactate steady state), “weekend warrior” (WW, n=13, 2 consecutive days per week for 75 min at the same intensity as REG), “fat burner” (FB, n=13, 5 sessions per week at a heart rate [HR] 15 min−1 below REG intensity), and control (CO, n=13, no training). Total energy output was held constant between the training groups which implied prolonging session durations for FB on an individual basis by 5 to 15 min to match the two other training groups. Training was conducted over 12 weeks and each session monitored by means of portable heart rate recorders. Identical graded treadmill protocols with simultaneous gas exchange, HR, and lactate measurements prior to and after the training program served for exercise prescription (given as HR ranges of 5–10 min−1) and documentation of endurance effects. RESULTS VO2max improved similarly and in all 3 training groups (REG +1.52 ml*min−1*kg−1, WW +3.37 ml*min−1*kg−1, FB +1.77 ml*min−1*kg−1). This effect was significant compared with CO (−0.95 ml*min−1*kg−1; p<0.05 for FB and REG; p<0.01 for WW). In comparison with CO (decrease by 3 min−1), average HR during incremental treadmill exercise decreased significantly by 9 min−1 (REG, p<0.05), 11 min−1 (WW, p<0.01), and 6 min−1 (FB, p<0.05). Only for the observed rightward shift of the lactate performance relationship, one group (FB) did not reach significant differences to CO. In absolute terms, the largest training gains were documented in WW. However, differences to the other training groups remained insignificant throughout. CONCLUSIONS In a middle-age population, deviations from commonly recommended weekly scheduling of training or from the choice of moderate intensity does not lead to major impairment of expectable improvements in endurance capacity provided the energy output is held equal. There are slight indications that the choice of a too low intensity might be more detrimental to positive training effects than piling up training sessions at the weekends as it is often practiced due to occupational constraints.

Effect of 6 weeks of endurance training on the lactate minimum speed

The aim of this study was to assess the sensitivity of the lactate minimum speed test to changes in endurance fitness resulting from a 6 week training intervention. Sixteen participants (mean +/- s :age 23 +/- 4 years;body mass 69.7 +/- 9.1 kg) completed 6 weeks of endurance training. Another eight participants (age 23 +/- 4 years; body mass 72.7 +/-12.5 kg) acted as non-training controls. Before and after the training intervention, all participants completed: (1) a standard multi-stage treadmill test for the assessment of VO 2max , running speed at the lactate threshold and running speed at a reference blood lactate concentration of 3 mmol.l -1 ; and (2) the lactate minimum speed test, which involved two supramaximal exercise bouts and an 8 min walking recovery period to increase blood lactate concentration before the completion of an incremental treadmill test. Additionally, a subgroup of eight participants from the training intervention completed a series of constant-speed runs for determination of running speed at the maximal lactate steady state. The test protocols were identical before and after the 6 week intervention. The control group showed no significant changes in VO 2max , running speed at the lactate threshold, running speed at a blood lactate concentration of 3 mmol.l -1 or the lactate minimum speed.In the training group, there was a significant increase in VO 2max (from 47.9 +/- 8.4 to 52.2 +/- 2.7 ml.kg -1 .min -1 ), running speed at the maximal lactate steady state (from 13.3 +/- 1.7 to 13.9 +/- 1.6 km.h -1 ), running speed at the lactate threshold (from 11.2 +/- 1.8 to 11.9 +/- 1.8 km.h -1 ) and running speed at a blood lactate concentration of 3 mmol.l -1 (from 12.5 +/- 2.2 to 13.2 +/- 2.1 km.h -1 ) (all P ≪ 0.05). Despite these clear improvements in aerobic fitness, there was no significant difference in lactate minimum speed after the training intervention (from 11.0 +/- 0.7 to 10.9 +/- 1.7 km.h -1 ). The results demonstrate that the lactate minimum speed,when assessed using the same exercise protocol before and after 6 weeks of aerobic exercise training, is not sensitive to changes in endurance capacity.

Submaximal Blood Lactate and Heart Rate Measurements as Indicators of Training Status in College Distance Runners

Seven highly trained male college distance runners were studied throughout a competitive cross-country season. Common laboratory and field measurements were used to assess their physiological adaptation to training. They were tested before (pre), during (mid), and at the end of the competitive season (post) for peak oxygen consumption (O2peak), running economy (RE), fractional utilization of the aerobic capacity (%O2peak), and time to exhaustion (TTE). One or 2 days prior to each scheduled competition, submaximal heart rate (HR) and submaximal blood lactate accumulation (bLa) were determined during a 1.61-km (1 mile) run on an indoor track. Five subjects ran at a 17.6-km · hr−1 pace while the other 2 ran at a 16.1-km · hr−1 pace, which corresponded to an estimated mean (±SE) intensity of 83.1% (±4.4) of preseason O2peak. O2peak, RE, %O2peak, and TTE all improved significantly over the season (p < 0.05). The field measures of HR and bLa remained unchanged during this same period. These results suggest that the field trials employing single HR and single bLa measurements (<80–85% O2peak) were not sensitive to changes in endurance capacity in 7 highly trained distance runners.

Effects of long-term, self-monitored exercise on the serum lipoprotein and apolipoprotein profile in middle-aged men

To study the effects of long-term, self-monitored exercise on the serum lipid profile and body composition of middle-aged non-smoking males, a controlled study was conducted in 61 sedentary, middle-class Swiss men. Thirty-nine men were randomly allocated to jog 2 h/wk for 4 months on an individually prescribed, heart rate-controlled basis, whereas 22 men served as controls. Despite varying adherence to the exercise regimen, the following 4-month net changes (effect in exercise group minus effect in control group) in lipids were seen: HDL cholesterol (C) + 0.12 mmol/l (95% CI 0.02, 0.22; fP = 0.028), LDL-C +0.08 mmol/1 (ns), VLDL-C -0.26 mmol/1 (-0.45, -0.07; P=0.009), total triglycerides (TT) −0.21 mmol/1 (ns), HDL-C/total C +0.02 (0.001, 0.05; P = 0.047). The net changes in endurance capacity and resting heart rate in favour of exercisers were significant as well, whereas no significant changes in apolipoprotein levels were seen. Exploratory analyses revealed, for example, associations of the increase in total physical activity with an increase in the HDL-C/total C ratio ( r = 0.46; P < 0.001), and of the change in estimated body fat content with an opposed change in the HDL-C/total C ratio ( r = -0.40; P < 0.001), or an inverse relationship of the change in subcutaneous fat with a change in the HDL 2-C level ( r = -0.39; P < 0.001). Multivariable regression analysis suggested that much of the effect of jogging on HDL-C was apparently mediated through a decrease in body fat content. A change in the waist/hip ratio was unrelated to lipoprotein changes but was related to the change of TT level ( r = 0.22; P < 0.05). This study confirms that individually prescribed, unsupervised jogging can increase HDL-C levels and improve the serum lipoprotein profile in self-selected nonsmoking males. Although the effect is modest, it may be relevant to preventive cardiology, given the evidence for a reduction in cardiovascular risk even after apparently small decreases in risk factor levels.