Jeanne Dekerle

Why does exercise terminate at the maximal lactate steady state intensity

Objective: The purpose of this study was to measure physiological responses during exercise performed until exhaustion at the exercise intensity corresponding to the maximal lactate steady state (MLSS) in order to determine why subjects stopped. Methods: Eleven male trained subjects performed a test at MLSS on a cycle ergometer until exhaustion. Results: Time to exhaustion was 55.0 (SD 8.5) min. No variation was observed between the 10th and the last minute for arterial pyruvate, bicarbonate, and haemoglobin concentrations, redox state, arterial oxygen pressure, arterial oxygen saturation, osmolality, haematocrit, oxygen uptake, carbon dioxide output, and gas exchange ratio (p>0.05). Arterial lactate concentration and arterial carbon dioxide pressure decreased significantly whereas pH, base excess and the Ratings of Perceived Exertion (RPE) increased significantly (p<0.05). Although respiratory rate, minute ventilation and heart rate increased significantly until exhaustion (p<0.05), values at termination of the MLSS test were significantly lower than values measured during a maximal exercise test (p<0.05). Blood ammonia concentrations rose progressively during the MLSS test. However, there is no known mechanism by which this change could cause peripheral fatigue. Conclusions: Exercise termination was not associated with evidence of failure in any physiological system during prolonged exercise performed at MLSS. Thus the biological mechanisms of exercise termination at MLSS were compatible with an integrative homoeostatic control of peripheral physiological systems during exercise.

Characterising the slope of the distance–time relationship in swimming

The aim of the present study was to assess whether the critical speed calculated by the slope of the distance-time relationship (S(d-t)) represents the boundary between the heavy and severe intensity domains in swimming and would be sustainable during intermittent exercise. Nine competitive male swimmers (mean+/-SD: aged 21.2+/-2.6 yrs; peak (.)VO2 of 3866+/-529 mL min(-1)) performed, (a) four fixed-distance (100-200-400-800 m) all-out efforts to determine S(d-t) and peak (.)VO2; (b) three constant-speed efforts to exhaustion (TTE) at and 5% above and below S(d-t) (S(d-t)(+5%) and S(d-t)(-5%), respectively); (c) a set of 10 x 400 m at S(d-t) with 40-s recovery in between. Capillary blood lactate concentration ([La](B)), oxygen uptake ((.)VO2), and RPE remained stable at S(d-t)(-5%) (TTE=48.9+/-14.1 min) with end values of 3.8+/-1.9 mmol L(-1), 87+/-14% peak (.)VO2, and 4.7+/-1.3. TTE decreased at S(d-t)(+5%) (8.6+/-3.1 min), with end [La](B) of 10.2+/-1.9 mmol L(-1). Peak (.)VO2 was reached at exhaustion. Similarly, S(d-t) could only be maintained for 24.3+/-7.7 min with an increase in RPE and [La](B), (.)VO2 reaching its peak (95+/-5% peak VO2). RPE increased but [La](B) remained stable throughout the ten 400 m blocks performed at S(d-t) (overall time of 53.9+/-2.7 min). The physiological responses when swimming 5% below and 5% above S(d-t) are those characterising the heavy and severe intensity domain, respectively. While S(d-t) lies within the severe intensity domain, intermittent swims at this intensity induce [La](B) steady state alongside high rates of perceived exertion.

Kinematic measures and stroke rate variability in elite female 200-m swimmers in the four swimming techniques: Athens 2004 Olympic semi-finalists and French National 2004 Championship semi-finalists

Abstract The aim of this study was to assess stroke rate variability in elite female swimmers (200-m events, all four techniques) by comparing the semi-finalists at the Athens 2004 Olympic Games (n = 64) and semi-finalists at the French National 2004 Championship (n = 64). Since swimming speed (V) is the product of stroke rate (SR) and stroke length (SL), these three variables and the coefficient of variation of stroke rate (CVSR) of the first and second 100 m were determined (V1, V2; SR1, SR2; SL1, SL2; CVSR1, CVSR2) and differences between the two parts of the events were calculated (ΔV; ΔSR; ΔSL; ΔCVSR). When the results for the four 200-m events were analysed together, SR1, SR2, SL1, and SL2 were higher (α = 0.05, P < 0.001) and ΔV, ΔSR, and ΔCVSR were lower (P < 0.01) in the Olympic group than in the National group. The Olympic-standard swimmers exhibited faster backstrokes and longer freestyle strokes (P < 0.05). Both CVSR1 and CVSR2 were lower for freestyle and backstroke races in the Olympic group than in the National group (P < 0.001). Our results suggest that stroke rate variability is dependent on an interaction between the biomechanical requisites of the task (techniques) and the standard of the swimmer.

Changes in swimming technique during time to exhaustion at freely chosen and controlled stroke rates

Abstract The aim of this study was to assess technical changes during constrained swimming in time-to-exhaustion tests. Ten swimmers of national standard performed a maximal 400-m front crawl and two sets of exhaustion tests at 95%, 100%, and 110% of mean 400-m speed. In the first set (free), swimmers had to maintain their speeds until exhaustion and mean stroke rate was recorded for each test. In the second set (controlled), the same speed and individual corresponding stroke rate were imposed. The durations of the exhaustion tests, relative durations of the stroke phases, and arm coordination were analysed. For each speed in the “controlled” set, the exhaustion tests were shorter. Moreover, variables were consistent, suggesting a stabilization of stroke technique. Under the free condition, stroke rate increased to compensate for the decrease in stroke length. At the same time, swimmers reduced the relative duration of their non-propulsive phases in favour of the propulsive phases. Thus, swimmers changed their arm coordination, which came close to an opposition mode. These two constraints enable swimmers both to maintain their stroking characteristics and develop compensatory mechanisms to maintain speed. Moreover, stroke rate can be seen as a useful tool for controlling arm technique during paced exercise.

Exercise-induced metabolic fluctuations influence AMPK, p38-MAPK and CaMKII phosphorylation in human skeletal muscle

During transition from rest to exercise, metabolic reaction rates increase substantially to sustain intracellular ATP use. These metabolic demands activate several kinases that initiate signal transduction pathways which modulate transcriptional regulation of mitochondrial biogenesis. The purpose of this study was to determine whether metabolic fluctuations per se affect the signaling cascades known to regulate peroxisome proliferator‐activated receptor γ coactivator‐1α (PGC‐1α). On two separate occasions, nine men performed a continuous (30‐min) and an intermittent exercise (30 × 1‐min intervals separated by 1‐min of recovery) at 70% of V˙O2peak . Skeletal muscle biopsies from the vastus lateralis were taken at rest and at +0 h and +3 h after each exercise. Metabolic fluctuations that correspond to exercise‐induced variation in metabolic rates were determined by analysis of VO2 responses. During intermittent exercise metabolic fluctuations were 2.8‐fold higher despite identical total work done to continuous exercise (317 ± 41 vs. 312 ± 56 kJ after intermittent and continuous exercise, respectively). Increased phosphorylation of AMP‐activated protein kinase (AMPK) (~2.9‐fold, P < 0.01), calcium/calmodulin‐dependent protein kinase II (CaMKII) (~2.7‐fold, P < 0.01) and p38‐mitogen‐activated protein kinase (MAPK) (~4.2‐fold, P < 0.01) occurred immediately in both exercises and to a greater extent after the intermittent exercise (condition x time interaction, P < 0.05). A single bout of intermittent exercise induces a greater activation of these signaling pathways regulating PGC‐1α when compared to a single bout of continuous exercise of matched work and intensity. Chronic adaptations to exercise on mitochondria biogenesis are yet to be investigated.

Exercise Tolerance Can Be Enhanced through a Change in Work Rate within the Severe Intensity Domain: Work above Critical Power Is Not Constant

Introduction The characterization of the hyperbolic power-time (P-t lim) relationship using a two-parameter model implies that exercise tolerance above the asymptote (Critical Power; CP), i.e. within the severe intensity domain, is determined by the curvature (W’) of the relationship. Purposes The purposes of this study were (1) to test whether the amount of work above CP (W>CP) remains constant for varied work rate experiments of high volatility change and (2) to ascertain whether W’ determines exercise tolerance within the severe intensity domain. Methods Following estimation of CP (208 ± 19 W) and W’ (21.4 ± 4.2 kJ), 14 male participants (age: 26 ± 3; peak V˙O2: 3708 ± 389 ml.min-1) performed two experimental trials where the work rate was initially set to exhaust 70% of W’ in 3 (‘THREE’) or 10 minutes (‘TEN’) before being subsequently dropped to CP plus 10 W. Results W>CP for TEN (104 ± 22% W’) and W’ were not significantly different (P>0.05) but lower than W>CP for THREE (119 ± 17% W’, P<0.05). For both THREE (r = 0.71, P<0.01) and TEN (r = 0.64, P<0.01), a significant bivariate correlation was found between W’ and t lim. Conclusion W>CP and t lim can be greater than predicted by the P-t lim relationship when a decrement in the work rate of high-volatility is applied. Exercise tolerance can be enhanced through a change in work rate within the severe intensity domain. W>CP is not constant.

The critical power concept in all-out isokinetic exercise

UNLABELLED The critical power concept has been applied to constant-load exhaustive exercise and recently validated for 3-min all-out exercise. OBJECTIVES To test the application of critical power to a 3-min all-out isokinetic cycling exercise. DESIGN Single-group, experimental, comparative design. METHOD Nine participants performed a 3-min all-out isokinetic test and 4-5 constant-load exhaustive trials, at 60 and 100 rpm, on an electrically-braked cycle. The linear P-t-1 relationship was modelled using a 2-parameter model (slope: critical power; intercept: Anaerobic Work Capacity). End power and accumulated work done above EP were calculated from the 3-min tests. RESULTS No significant difference and a significant correlation was found between end power and critical power (60 rpm: 259 ± 40 W vs. 245 ± 38 W, P > 0.05; r = 0.85, P<0.01; 100 rpm: 227 ± 57 W vs. 212 ± 44 W, P > 0.05; r = 0.86, P<0.01). The Bias ± 95% limits of agreement were 14 ± 42 W at 60 rpm and 15 ± 57 W at 100 rpm. Work done above EP (60 rpm: 14.7 ± 3.0 kJ; 100 rpm: 17.3 ± 3.1 kJ) was not significantly different to the anaerobic work capacity (60 rpm: 16.2 ± 3.2 kJ; 100 rpm: 20.6 ± 6.4 kJ; P>0.05) but with only a significant correlation at 60 rpm (r = -0.71, P<0.05). CONCLUSIONS The 2-parameter model underpinning the critical power construct can be applied to a 3-min all-out isokinetic test. End power does not differ and correlates with critical power. However, a further insight into levels of agreement leads to some scepticism concerning the use of the two variables interchangeably. The great intra-subject differences between work done above EP and the intercept of the P-t-1 relationship should also be considered.

Effect of aerobic training status on both maximal lactate steady state and critical power

This study aimed at assessing the sensitivity of both maximal lactate steady state (MLSS) and critical power (CP) in populations of different aerobic training status to ascertain whether CP is as sensitive as MLSS to a change in aerobic fitness. Seven untrained subjects (UT) (maximal oxygen uptake = 37.4 ± 6.5 mL·kg(-1)·min(-1)) and 7 endurance cyclists (T) (maximal oxygen uptake = 62.4 ± 5.2 mL·kg(-1)·min(-1)) performed an incremental test for maximal oxygen uptake estimation and several constant work rate tests for MLSS and CP determination. MLSS, whether expressed in mL·kg(-1)·min(-1) (T: 51.8 ± 5.7 vs. UT: 29.0 ± 6.1) or % maximal oxygen uptake (T: 83.1 ± 6.8 vs. UT: 77.1 ± 4.5), was significantly higher in the T group. CP expressed in mL·kg(-1)·min(-1) (T: 56.8 ± 5.1 vs. UT: 33.1 ± 6.3) was significantly higher in the T group as well but no difference was found when expressed in % maximal oxygen uptake (T: 91.1 ± 4.8 vs. UT: 88.3 ± 3.6). Whether expressed in absolute or relative values, MLSS is sensitive to aerobic training status and a good measure of aerobic endurance. Conversely, the improvement in CP with years of training is proportional to those of maximal oxygen uptake. Thus, CP might be less sensitive than MLSS for depicting an enhancement in aerobic fitness.

Critical power is not attained at the end of an isokinetic 90-second all-out test in children

Abstract The purpose of this study was to establish whether critical power, as traditionally determined from the performance of three constant-load tests to exhaustion, is attained at the end of a 90-s all-out test in children. Sixteen healthy children (eight males and eight females; mean age 12.3 years, sx = 0.1; body mass 39.6 kg, sx = 1.8; peak [Vdot]O2 2.0 litres · min−1, sx = 0.1) completed an incremental test to exhaustion to determine peak oxygen uptake (peak [Vdot]O2), three separate constant-load tests to exhaustion to calculate critical power, and an isokinetic 90-s all-out test. The end power of the 90-s test averaged over the last 10 s (140 W, sx = 8) was significantly higher than critical power (105 W, sx = 6; t = 6.8; P < 0.01), yet the two parameters were strongly correlated (r = 0.74; P < 0.01). After 60 s, there were no further reductions in power output during the 90-s test (P < 0.0001). In conclusion, at the end of a 90-s all-out test, children are able to produce power outputs well above critical power. This suggests that 90 s is not long enough to completely exhaust the anaerobic work capacity in children.

Effect of stroke rate reduction on swimming technique during paced exercise.

Alberty, MR, Potdevin, FP, Dekerle, J, Pelayo, PP, and Sidney, MC. Effect of stroke rate reduction on swimming technique during paced exercise. J Strength Cond Res 25(2): 392-397, 2011-The purpose of this study is to analyze the acute adaptations of motor organization subsequent to a reduction in spontaneous stroke rate (SR) at different swimming speeds, a task constraint that is currently used by trainers to improve stroke technique. Ten well-trained swimmers (8 males and 2 females, whose mean swimming speed on a 400-m front crawl stroke represents 76.8 ± 3.7% and 73.3 ± 2.7% of the mean speed of the short-course pool world record, respectively) performed 3 sets of 3 time to exhaustion trials in front crawl at paces corresponding to 95%, 100%, and 110% of the mean speed measured in a 400-m race. During the first set, individual SR was continuously recorded and averaged. During the second set (Fixed), participants were constrained to swim at their individual corresponding SR. For the third set (Lowered), an individual corresponding SR value lowered by 5% was imposed. Durations of trials and arm stroke phases durations were analyzed. The results showed that the durations of the whole trials declined significantly from the Fixed set to the Lowered set (p < 0.05). Swimmers spent more time in the nonpropulsive phases (increases ranged from 8.6-13.2%; p < 0.05), and the duration of the propulsive phases did not differ significantly in the lowered set. The significant decline in exercise durations might have been caused by an unusual muscular solicitation. Swimming technique changes during trials in the Fixed set suggest an increase in magnitude and efficiency in the propulsive force and a better body streamlining to limit an increase of the resistive impulse in between arm propelling actions. In conclusion, these results should be taken into account to better define training-set technical benefits and better include the impact of such task constraints into the training schedule.