Patrick Legros

Methods to Determine Aerobic Endurance

AbstractPhysiological testing of elite athletes requires the correct identification and assessment of sports-specific underlying factors. It is now recognised that performance in long-distance events is determined by maximal oxygen uptake (.VO2max), energy cost of exercise and the maximal fractional utilisation of.VO2max in any realised performance or as a corollary a set percentage of.VO2max that could be endured as long as possible. This later ability is defined as endurance, and more precisely aerobic endurance, since.VO2max sets the upper limit of aerobic pathway. It should be distinguished from endurance ability or endurance performance, which are synonymous with performance in long-distance events. The present review examines methods available in the literature to assess aerobic endurance. They are numerous and can be classified into two categories, namely direct and indirect methods. Direct methods bring together all indices that allow either a complete or a partial representation of the power-duration relationship, while indirect methods revolve around the determination of the so-called anaerobic threshold (AT). With regard to direct methods, performance in a series of tests provides a more complete and presumably more valid description of the power-duration relationship than performance in a single test, even if both approaches are well correlated with each other. However, the question remains open to determine which systems model should be employed among the several available in the literature, and how to use them in the prescription of training intensities. As for indirect methods, there is quantitative accumulation of data supporting the utilisation of the AT to assess aerobic endurance and to prescribe training intensities. However, it appears that: (i) there is no unique intensity corresponding to the AT, since criteria available in the literature provide inconsistent results; and (ii) the non-invasive determination of the AT using ventilatory and heart rate data instead of blood lactate concentration ([La- ]b) is not valid. Added to the fact that the AT may not represent the optimal training intensity for elite athletes, it raises doubt on the usefulness of this theory without questioning, however, the usefulness of the whole [La- ]b-power curve to assess aerobic endurance and predict performance in long-distance events.

Blood lactate response to overtraining in male endurance athletes

Abstract Many physiological markers vary similarly during training and overtraining. This is the case for the blood lactate concentration ([La−]b), since a right shift of the lactate curve is to be expected in both conditions. We examined the possibility of separating the changes in training from those of overtraining by dividing [La−]b by the rating of perceived exertion ([La−]b/RPE) or by converting [La−]b into a percentage of the peak blood lactate concentration ([La−]b,peak). Ten experienced endurance athletes increased their usual amount of training by 100% within 4 weeks. An incremental test and a time trial were performed before (baseline) and after this period of overtraining, and after 2 weeks of recovery (REC). The [La−]b and RPE were measured during the recovery of each stage of the incremental test. We diagnosed overtraining in seven athletes, using both physiological and psychological criteria. We found a decrease in mean [La−]b,peak from baseline to REC [9.64 (SD 1.17), 8.16 (SD 1.31) and 7.69 (SD 1.84) mmol · l−1, for the three tests, respectively; P < 0.05] and a right shift of the lactate curve. Above 90% of maximal aerobic speed (MAS) there was a decrease of mean [La−]b/RPE from baseline to REC [at 100% of MAS of 105.41 (SD 17.48), 84.61 (SD 12.56) and 81.03 (SD 22.64) arbitrary units, in the three tests, respectively; P < 0.05), but no difference in RPE, its variability accounting for less than 25% of the variability of [La−]b/RPE (r=0.49). Consequently, [La−]b/RPE provides little additional information compared to [La−]b alone. Expressing [La−]b as a %[La−]b,peak resulted in a suppression of the right shift of the lactate curve, suggesting it was primarily the consequence of a decreased production of lactate by the muscle. Since the right shift of the curve induced by optimal training is a result of improved lactate utilization, the main difference between the two conditions is the decrease of [La−]b,peak during overtraining. We propose retaining it as a marker of overtraining for long duration events, and repeating its measurement after a sufficient period of rest to make the distinction with overreaching.

Optimal whole-body vibration settings for muscle strength and power enhancement in human knee extensors.

This study compared the effects of 6-week whole-body vibration (WBV) training programs with different frequency and peak-to-peak displacement settings on knee extensor muscle strength and power. The underlying mechanisms of the expected gains were also investigated. Thirty-two physically active male subjects were randomly assigned to a high-frequency/high peak-to-peak displacement group (HH; n=12), a low-frequency/low peak-to-peak displacement group (LL; n=10) or a sham training group (SHAM; n=10). Maximal voluntary isometric, concentric and eccentric torque of the knee extensors, maximal voluntary isometric torque of the knee flexors, jump performance, voluntary muscle activation, and contractile properties of the knee extensors were assessed before and after the training period. Significant improvement in knee extensor eccentric voluntary torque (P<0.01), knee flexor isometric voluntary torque (P<0.05), and jump performance (P<0.05) was observed only for HH group. Regardless of the group, knee extensor muscle contractile properties (P<0.05) were enhanced. No modification was observed for voluntary muscle activation or electrical activity of agonist and antagonist muscles. We concluded that high-frequency/high peak-to-peak displacement was the most effective vibration setting to enhance knee extensor muscle strength and jump performance during a 6-week WBV training program and that these improvements were not mediated by central neural adaptations.

Whole-body vibration training effects on the physical performance of basketball players.

Colson, SS, Pensini, M, Espinosa, J, Garrandes, F, and Legros, P. Whole-body vibration training effects on the physical performance of basketball players. J Strength Cond Res 24(4): 999-1006, 2010-The aim of this study was to investigate the influence of 4 weeks of whole-body vibration training added to the conventional training of basketball players. Eighteen competitive basketball players (13 ♂, 5 ♀, 18-24 years old) were randomly assigned to a whole-body vibration group (WBVG, n = 10; 7 ♂ and 3 ♀) or a control group (CG, n = 8; 6 ♂ and 2 ♀). During the 4-week period, all subjects maintained their conventional basketball training program. The members of WBVG were additionally trained 3 times a week for 20 minutes on a vibration platform (10 unloaded static lower limb exercises, 40-Hz, 4-mm, Silverplate®). Testing was performed before and after the 4-week period and comprised strength assessment, vertical jump performance, and a 10-m sprint test. The maximal voluntary isometric strength of the knee extensors significantly increased (p < 0.001) after vibration training, as did squat jump (SJ) height (p < 0.05), whereas performance of the countermovement jump, drop jump, 30-second rebound jump, and 10-m sprint remained unchanged. The results of the present study indicated that a 4-week whole-body vibration training program added to the conventional training of basketball players during the preseason is an effective short-term stimulus to enhance knee extensor strength and slightly SJ performance.

Variability in energy cost and walking gait during race walking in competitive race walkers

PURPOSE The aim of this study was to examine the variability of energy cost (Cw) and race walking gait after a 3-h walk at the competition pace in race walkers of the same performance level. METHODS Nine competitive race walkers were studied. In the same week, after a first test of VO2max determination, each subject completed two submaximal treadmill walks (6 min length, 0% grade, 12 km X h(-1) speed) before and after a 3-h overground test completed at the individual competition speed of the race walker. During the two submaximal tests, subjects were filmed between the 2nd and the 4th min, and physiological parameters were recorded between the 4th and the 6th min. RESULTS Results showed two trends. On the one hand, we observed a significant and systematic increase in energy cost of walking (mean deltaCw = 8.4%), whereas no variation in the gait kinematics prescribed by the rules of race walking was recorded. On the other hand, this increase in metabolic energy demand was accompanied by variations of different magnitude and direction of stride length, of the excursion of the heel and of the maximal ankle flexion at toe-off among the race walkers. CONCLUSION These results indicated that competitive race walkers are able to maintain their walking gait with exercise duration apart from a systematic increase in energy cost. Moreover, in this form of locomotion the effect of fatigue on the gait variability seems to be an individual function of the race walk constraints and the constraints of the performer.

SEMG power spectrum changes during a sustained 50% Maximum Voluntary Isometric Torque do not depend upon the prior knowledge of the exercise duration.

Endurance time (Tlim) is a relevant indicator of muscular resistance to fatigue. It has been recently shown that SEMG changes computed during shorter periods (sub-maximal durations) than the whole test duration could serve to predict Tlim. The aim of the present study was to test whether the prior knowledge of the sub-maximal duration had any influence on Tlim prediction throughout SEMG changes. For this purpose, we compared myoelectric changes estimated over a 30-s isometric contraction whose duration was known by the subjects, to those changes measured during the first 30 s of a test prolonged until exhaustion. The effort intensity was set at 50% of the maximal voluntary isometric torque (MVIT). The myoelectric manifestations of muscle fatigue appeared to change in a similar way during both sessions for temporal and spectral analyses. In conclusion, the prior knowledge of the duration of sustained isometric contraction did not influence the motor unit recruitment strategy throughout surface EMG evaluation. These results confirmed that the use of SEMG changes computed over shorter periods than expected endurance time may be applied to investigate the capability of the initial rate of SEMG changes to predict muscle endurance capacity at 50%MVIT. This may be of particular interest for patient evaluation in the clinical field.

Knee isometric torque and electromyographic specificities after semitendinosus and gracilis hamstrings anterior cruciate ligament reconstruction.

Garrandes F, Colson SS, Parisaux J-M, Legros P: Knee isometric torque and electromyographic specificities after semitendinosus and gracilis hamstrings anterior cruciate ligament reconstruction. Am J Phys Med Rehabil 2006;85:127–134. Objectives:Because the co-contraction of the gastrocnemius and hamstring muscles strains the anterior cruciate ligament, the role of the gastrocnemius muscle is of particular importance after semitendinosus and gracilis tendon autografts for anterior cruciate ligament reconstruction. This study aimed to examine the neuromuscular mechanisms underlying postsurgical torque deficits during knee flexion by using surface electromyography. Design:A total of 14 volunteer patients (eight men, six women; age, 32.5 ± 9.3 yrs; height, 172.7 ± 6 cm; weight, 69.6 ± 10.2 kg) were enrolled in the study; all had undergone anterior cruciate ligament reconstruction performed by the same surgeon. The neuromuscular mechanisms were assessed using isometric tests and surface electromyographic recordings at 19 mos postreconstruction. The torque deficits in the injured knee were compared with the uninjured knee, which served as control values. Results:Significant differences in torque production were observed between the two limbs at specific angular positions during the extension and flexion tests (P < 0.05). The difference in the root mean square myoelectrical activity between the limbs was computed at each tested position, revealing that the gastrocnemius muscle had greater activity at 75 degrees than at 45 degrees (P < 0.05). Conclusions:In deep flexion (>70 degrees), the gastrocnemius muscle may compensate for the weakened hamstrings and thereby strain the anterior cruciate ligament graft after anterior cruciate ligament semitendinosus and gracilis tendon reconstruction.

Neuromuscular fatigue kinetics are sport specific

Mechanisms underlying fatigue are commonly divided into two components. Central fatigue, involves insufficient neural drive to the muscle, and peripheral fatigue includes changes beyond the neuromuscular junction. The nature of fatiguing exercise influences the mechanical and neuromuscular parameters. This has been termed “task dependency” (Enoka and Stuart, 1992). Several studies have reported the influence of contraction mode (concentric vs eccentric), intensity, and duration use in fatiguing exercise on neuromuscular alterations (Pasquet et al. 2000). Other studies reported the influence of activity performed during the test on fatigue level (Millet and Lepers 2004). However, there is a lack of knowledge concerning the influence on fatigue of sport specificity. The purpose of this study was to determine whether fatigue kinetics and fatigue origin (central vs. peripheral adaptations) of the knee extensor muscles are sport specific.