Modelling of Running Performances: Comparisons of Power-Law, Hyperbolic, Logarithmic, and Exponential Models in Elite Endurance Runners.

Many empirical and descriptive models have been proposed since the beginning of the 20th century. In the present study, the power-law (Kennelly) and logarithmic (Péronnet-Thibault) models were compared with asymptotic models such as 2-parameter hyperbolic models (Hill and Scherrer), 3-parameter hyperbolic model (Morton), and exponential model (Hopkins). These empirical models were compared from the performance of 6 elite endurance runners (P. Nurmi, E. Zatopek, J. Väätäinen, L. Virén, S. Aouita, and H. Gebrselassie) who were world-record holders and/or Olympic winners and/or world or European champions. These elite runners were chosen because they participated several times in international competitions over a large range of distances (1500, 3000, 5000, and 10000 m) and three also participated in a marathon. The parameters of these models were compared and correlated. The less accurate models were the asymptotic 2-parameter hyperbolic models but the most accurate model was the asymptotic 3-parameter hyperbolic model proposed by Morton. The predictions of long-distance performances (maximal running speeds for 30 and 60 min and marathon) by extrapolation of the logarithmic and power-law models were more accurate than the predictions by extrapolation in all the asymptotic models. The overestimations of these long-distance performances by Morton's model were less important than the overestimations by the other asymptotic models.

Relationship between vertical jump and maximal power output of legs and arms: effects of ethnicity and sport.

The hypothesis that ethnicity and sport practice influence the relationship between maximal power in cycling (P(max)) and countermovement jump (CMJ) has been studied by relating CMJ and P(max) in two groups (volleyball players, VB, and physical education students, PES) including subjects with Caucasian (67 C) or West African (39 WA) origins. Maximal power of the arms (P(max) Arms) was also measured. A two-way analysis of variance (groups × ethnicity) showed significant effects of both factors upon CMJ, which was higher in WA and VB, P = 0.002 and P < 0.001, respectively. Within WA, CMJ was significantly higher in VB (0.732 ± 0.057 m) than in PES (0.661 ± 0.082 m), although there was no difference in P(max) (14.7 ± 1.7 vs 14.7 ± 1.9 W/kg). CMJ was significantly higher in WA (0.69 ± 0.08 vs 0.65 ± 0.09 m in C, P = 0.002) without significant interethnic difference in P(max) (14.7 ± 1.8 in WA, and 14.8 ± 1.9 W/kg in C). The CMJ-P(max) relationships were different in C and WA (P = 0.003). Therefore, CMJ predicted from P(max) would be underestimated in WA. The same difference was observed for the relationship between CMJ and P(max) Arms. These results were confirmed by the comparison with previous P(max) -CMJ relationship in the literature, collected in Caucasian and African subjects with the same protocols.

Assessment of isokinetic knee strength in elite young female basketball players: correlation with vertical jump.

AIM: To explore the isokinetic concentric strength of the knee muscle groups, and the relationship between the isokinetic knee extensors strength and the vertical jump performance in young elite female basketball players. METHODS: Eighteen elite female basketball players performed a countermovement jump, and an isokinetic knee test using a Biodex dynamometer. The maximal isokinetic peak torque of the knee extensor and flexor muscles was recorded at four angular velocities (90°/s, 180°/s, 240°/s and 300°/s) for the dominant and non-dominant legs. The conventional hamstring/quadriceps ratio (H/Q) was assessed at each angular velocity for both legs. RESULTS: There was no significant difference between dominant and non-dominant leg whatever the angular velocity (all P>0.05). However, the H/Q ratio enhanced as the velocity increased from 180°/s to 300°/s (P<0.05). Furthermore, low to high significant positive correlations were detected between the isokinetic measures of the knee extensors and the vertical jump height. The highest one was found for the knee extensors peak torque at a velocity of 240°/s (r=0.88, P<0.001). CONCLUSION: The results accounted for an optimal velocity at which a strong relationship could be obtained between isokinetic knee extensors strength and vertical jump height. Interestingly, the H/Q ratio of the young elite female basketball players in the present study was unusual as it was close to that generally observed in regular sportsmen.

Cardiovascular responses during hypoventilation at exercise.

This study aimed to determine the cardiovascular responses during a prolonged exercise with voluntary hypoventilation (VH). 7 men performed 3 series of 5-min exercise at 65% of normoxic maximal O (2) uptake under 3 conditions: (1) normal breathing (NB) in normoxia (NB (0.21)), (2) VH in normoxia (VH (0.21)), (3) NB in hypoxia (NB (0.157), inspired oxygen fraction=0.157). In both VH (0.21) and NB (0.157), there was a similar drop in arterial oxygen saturation and arterial O (2) content (CaO (2)) which were lower than in NB (0.21). Heart rate (HR), stroke volume, and cardiac output (-) were higher in VH (0.21) than in NB (0.21) during most parts of exercise whereas there was no difference between NB (0.157) and VH (0.21) or NB (0.21). HR variability analysis suggested an increased sympathetic modulation in VH (0.21) only. O (2) transport and oxygen uptake were generally not different between interventions. Mixed venous O (2) content (C-O (2)) was lower in NB (0.157) than in both VH (0.21) and NB (0.21) and not different between the latter. CaO (2)-C-O (2) was not different between NB (0.157) and NB (0.21) but lower in VH (0.21). This study shows that a prolonged exercise with VH leads to a greater cardiac activity, independent from the hypoxic effect. The greater - in VH compared to normal breathing seems to be the main factor for compensating the drop of arterial oxygen content.

Oxygen uptake response to an 800-m running race.

We tested the hypothesis that time course of O (2) uptake (VO (2)) measured during a supramaximal exercise performed in the field is driven to maximal oxygen uptake (VO (2max)). On an outdoor track, five middle-distance male runners first performed a test to determine VO (2max) and a supramaximal 800-m running test at least two days apart. VO (2) response was measured from the start to the end of exercise with the use of a miniaturised telemetric gas exchange system (Cosmed K4). VO (2max) was reached by all subjects 45 +/- 11 s (mean +/- SD) after the onset of the 800-m race (i.e., 316 +/- 75 m), and was maintained during the next 33 +/- 6 s (i.e., 219 +/- 41 m). The mean relative exercise intensity of the 800 m was 120 % VO (2max). An unexpected significant decrease in VO (2) (24.1 +/- 7.0 %; p < 0.05) was observed in all subjects during the final 38 +/- 17 s (i.e., the last 265 +/- 104 m). We concluded that, at onset of a simulated 800 m running event, VO (2) is quickly projected towards the VO (2max), and then becomes limited by the achievable VO (2max). This race profile shown by all athletes is in some contrast to what can be expected from earlier findings in a laboratory setting.

[Oxygen uptake and maximal oxygen uptake: interests and limits of their measurements]. / Consommation d'oxygène et consommation maximale d'oxygène: intérêts et limites de leur mesure.

The paper presents a review of the interests and limits of oxygen uptake measurement in the functional testing of athletes and disabled people. The validity of the oxygen uptake as an estimation of the oxygen consumption and aerobic synthesis of ATP is discussed in the introduction of the review. The author discusses the interests of oxygen uptake measurements for the study of energy cost in addition to maximal oxygen uptake. The limits of the study of oxygen uptake kinetics at the beginning of exercise are discussed. The methodology of oxygen measurement is mainly focused on the characteristics of the different ergometers and the choice of an exercise protocol. The review ends with short statements related to the current knowledge on maximal oxygen uptake, its limiting factors and the effects of age, gender, body mass, active muscle mass and training.

Maximal voluntary force and rate of force development in humans--importance of instruction.

The present investigation has been designed to confirm the effect of instruction (hard-and-fast instruction compared to fast instruction) upon maximal voluntary isometric force (MVF) and maximal rate of force development (MRFD) in muscle groups which differ with regards to muscle mass and usage. In addition, we took advantage of the force data collected during unilateral and bilateral leg extension, to compare the instruction effects on the indices of the bilateral deficits (BI, the differences between the data collected during bilateral extensions and the sum of the data collected during unilateral left and right extensions) with regard to MVF (BIMVF) and MRFD (BIMRFD). Force-time curves were recorded during maximal isometric contractions of the elbow flexors, the leg extensors of the take-off and lead legs and during bilateral leg extension in 26 healthy young male volunteers from the track-and-field national team of Tunisia. In the first protocol, the subjects were instructed to produce MFV as hard-and-fast as possible (instruction I). In the second protocol (instruction II) the subjects were instructed to provide MFRD, that is the most explosive force, by concentrating on the fastest contraction without concern for achieving maximal force. The present study confirmed the importance of an appropriate instruction for the measurement of MRDF The MRFD (F = 40.8, P < 0.001) were significantly higher when measured after instruction II compared to instruction I. The effect of the instruction upon MRFD were similar for muscle groups with different volumes, cortical representations and uses. The same results (F = 52.1; P < 0.001) were observed when MRFD was related to MVF [MRFD% = (MRFD/MVF) x 100]. On the other hand, MVF was similar following both instructions (ANOVA, F = 0.562; P = 0.454). Moreover, the results of the present study suggested that the effect of instruction was significantly larger for BIMRFD than for BIMVF.

Effects of external loading on power output in a squat jump on a force platform: a comparison between strength and power athletes and sedentary individuals.

The aim of this study was to determine the effects of external loading on power output during a squat jump on a force platform in athletes specializing in strength and power events (6 elite weight-lifters and 16 volleyball players) and in 20 sedentary individuals. Instantaneous power was computed from time-force curves during vertical jumps with and without an external load (0, 5 or 10 kg worn in a special vest). The jumps were performed from a squat position, without lower limb counter-movement or an arm swing. Peak instantaneous power corresponded to the highest value of instantaneous power during jumping. Average power throughout the push phase of the jump was also calculated. A two-way analysis of variance showed significant interactions between the load and group effects for peak instantaneous power (P< 0.01) and average power (P< 0.001). Peak instantaneous power decreased significantly in sedentary individuals when moderate external loads were added. The peak instantaneous power at 0 kg was greater than that at 5 and 10 kg in the sedentary individuals. In contrast, peak instantaneous power was independent of load in the strength and power athletes. Mean power at 0 kg was significantly lower than at 5 kg in the athletes; at 0 kg it was significantly higher than at 10 kg in the sedentary males and at 5 and 10 kg in the sedentary females. In all groups, the force corresponding to peak instantaneous power increased and the velocity corresponding to peak instantaneous power decreased with external loading. The present results suggest that the effects of external loading on peak instantaneous power are not significant in strength and power athletes provided that the loads do not prevent peak velocity from being higher than the velocity that is optimal for maximal power output.

Critical power of knee extension exercises does not depend upon maximal strength.

A possible dependence of critical power (CP) and the Y-intercept of the work/exhaustion time relationship (Y(intercept)) on maximal muscular strength of the same muscle group has been studied in nine endurance-trained subjects, seven gymnasts, and seven weight-lifters. CP was calculated as being equal to the slope of the linear relationship between exhaustion time and the work performed at exhaustion on a knee extension ergometer. Y(intercept) was equal to the intercept between this relationship and the work axis. The muscular strength of the knee was evaluated by measuring the torques exerted on a Biodex knee isokinetic dynamometer at four angular velocities: 0 degrees x s(-1) (T0), 90 degrees x s(-1) (T90), 180 degrees x s(-1) (T180) and 240 degrees x s(-1) (T240). The results of the present study do not support the hypothesis that CP depends upon maximal strength. Indeed, CP was not correlated with T0, T90, T180 or T240 (¿r¿ < 0.01). Y(intercept) was significantly and positively correlated only with T90.

Local critical power is an index of local endurance.

The hypothesis that critical power (CP) is significantly lower than the maximal aerobic power of the knee extensors has been tested in nine endurance-trained subjects, seven gymnasts and seven weight lifters. CP was calculated as being equal to the slope of the linear relationship between exhaustion time and work performed at exhaustion on a knee-extension ergometer. CP was compared with the power output at the end of a progressive knee-extension exercise (P(peak)) and the power outputs corresponding to exhaustion times equal to 4 (P(4 min)), 6 (P(6 min)), 8 (P(8 min)) and 10 min (P(10 min)), calculated according to the linear relationship between work and exhaustion time. The hypothesis that CP corresponds to a steady state in metabolic and physiological parameters was tested in the gymnasts and the weight lifters by comparing CP with the fatigue thresholds of the integrated electromyogram (iEMG(FT)), lactate level (La(FT)), oxygen uptake (VO(2FT)) and heart rate (HR(FT)). The results of the present study demonstrate that the value of CP of a local exercise cannot be considered as the equivalent of the maximal aerobic power for general exercises. The values of P(4 min), P(6 min), P(8 min), P(10 min) and P(peak) were significantly higher than CP, and corresponded to 138, 126, 119, 115 and 151% CP, respectively. The results of the present study indicate that CP can be considered as an index of muscular endurance. Indeed, La(FT), iEMG (FT), VO(2FT) and HR(FT) were not significantly different from CP. All of these fatigue thresholds were significantly correlated with CP (r > 0.92). Moreover, the highest coefficient of correlation (r=0.71; P < 0.01) between the percentage of maximal aerobic power in cycling that corresponds to a blood lactate concentration of 4 mmol x l(-1) (OBLA%) and the different local aerobic indices was observed with CP.

Recovery of the torque-velocity relationship after short exhausting cycling exercise.

The effects of fatigue upon the torque-velocity (T-omega) relationship in cycling were studied in 11 subjects. Fatigue was induced by short exhausting exercise, on a cycle ergometer, consisting of 4 all-out sprints without recovery. The linear (T-omega) relationship was determined during each all-out sprint, before, during and after the exhausting exercise. The kinetics of the T-omega relationship had permitted the study of the recovery of optimal torque, optimal velocity and their corresponding maximal power outputs (Pmax), 30 s or 1 min after the short exhausting exercise. Fatigue induced a parallel shift to the left of the T-omega relationship which was partly reversed by a parallel shift to the right during recovery. After 30 s recovery optimal velocity, optimal torque and Pmax were slightly lower than the corresponding values before the exhausting exercise; after 1-min optimal velocity and optimal torque had recovered 99% and 97% of their initial values. These mechanical data suggested that the causes of exhaustion were processes that allowed fast recovery of both optimal velocity and optimal torque.

A new rating scale of perceived exertion based on subjective estimation of exhaustion time: a preliminary study.

Perceived exertion has been investigated during incremental exercise to exhaustion with athletes, according to the 6-20 scale proposed by Borg (RPE, 1970) and a new scale based on the estimation of exhaustion time (t(lim)) (Estimated Time Limit or ETL, from 1 to 20; ETL= 21 - 2 n, with n = log2t(lim)). ETL increased linearly with the percentage of maximal aerobic power (%MAP) up to the ventilatory threshold (VT). Beyond VT, an inflection of the ETL-%MAP relationship was observed. RPE and ETL calculated at VT were equal to 15 +/- 1.7, i.e. an exercise intensity perceived as "hard", and 10 +/- 2.3, i.e. an estimated exhaustion time equal approximately to 45 minutes. Standard deviations for RPE and ETL at VT were too large for an accurate estimation of this threshold. The results of the present study suggest that RPE and ETL should be used in addition to physiological data, but not replace them in the prescription of a training program.

Peak power and pulmonary oxygen uptake during knee extension exercise--comparisons among different incremental protocols.

Four incremental protocols of knee extension exercise of different stage durations were compared to study the effect of the protocol upon power output at the last stage (Ppeak). Previous studies of knee extension have found very different power outputs with similar ergometers and these large differences have been interpreted as being the result of the fatigue due to the durations of the protocols. The knee extension device used in previous studies was modified to avoid the action of the knee and hip flexors: the subjects pushing on a lever instead of pulling a rod. In the present study five subjects performed four incremental knee extension exercises which differed with regard to stage duration (60, 90, 180 or 360 s) on this ergometer. The Ppeak, peak oxygen uptake (VO2peak) and peak heart rate (HRpeak) were measured at the end of each of these four incremental protocols. In eight subjects, the reliability of the protocols with the two shortest increments (60 and 90-s stages) was verified by measuring Ppeak at 60 s and 90 s (Ppeak60, Ppeak90) twice. The knee ergometer proposed in the present paper was easy to use without any special training and should improve the measurement of Ppeak. The Ppeak60 [49.4 (SD 5.6) W] was higher than at 180 s [Ppeak180), 43.6 (SD 5.8) W, P < 0.05] and at 360 s [Ppeak360, 43.4 (SD 5.3) W, P < 0.05]. All the other differences in Ppeak, VO2 peak and HRpeak were not significant. All correlations between Ppeak60, Ppeak90, Ppeak180 and Ppeak360 were significant, except those between Ppeak360 and Ppeak90 or Ppeak180. The effect of the stage duration on power output and oxygen uptake at the end of the knee extension exercises was not great. Consequently, the large differences in power output and oxygen uptake observed in previous studies cannot be explained by the protocol only. The significant difference between Ppeak 60 and Ppeak90 was of the order of 10% in agreement with findings in the literature using cycle ergometry. The reliability of Ppeak60 and Ppeak90 was high and the use of these protocols can be recommended if further studies show that the measurement of Ppeak, is useful in the evaluation of local endurance.

Ratings of perceived exertion (RPE) during cycling exercises at constant power output.

The purpose of the present investigation was to study the overall rating of perceived exertion (RPEov) according to the 6-20 scale proposed by Borg (1970) and muscular RPE (RPEmu) in exercises at constant load. The relationship between RPE and heart rate for three different loads was studied during exhausting exercises in 10 participants. Whether the drift of RPE during a 20 min exercise at constant load could be an index of the endurance time during long-lasting exercises at constant load was also investigated. At 1-week intervals, the participants performed cycling exercises up to exhaustion at 60, 73, and 86% maximal aerobic power (MAP) measured during an incremental test. Heart rate, RPEov, RPEmu and exhaustion time (tlim) were measured. The upward shift of the HRmax-RPE regressions was significant between 86, 73 and 60% MAP (p < 0.001) for RPEov and RPEmu. This result suggests that the equation HR = 10 x RPE proposed by Borg (1973) for incremental exercise is not valid for long-lasting exercise at constant load until exhaustion because the heart rate corresponding to a given RPE depends on load and time. Mean RPE increased linearly with time up to exhaustion. Unexpectedly, the relationships between RPEmu or RPEov and percentage of exhaustion time were similar for exercises at 60 and 73% MAP although the exhaustion times were very different (79.40 +/- 30.64 min versus 36.19 +/- 15.99 min, respectively) (p < 0.001). Consequently, it is likely that RPE was a subjective estimation of the hardness of exercise rather than the intensity of exercise. The RPE pattern at the beginning of long-lasting exercises at constant load (60 and 73% MAP) cannot be considered as a sensitive predictor of the point of self-imposed exhaustion for individuals. Indeed, the errors in the estimation of exhaustion time from extrapolation of RPE at the beginning of exercise were very large. Moreover, at 60% MAP, a steady-state in RPE was observed during 20 min in five subjects whose tlim were not longer than tlim of the other subjects. In addition, the data of the present study indicate that RPEmu could be more useful than RPEov in cycling.

Ratings of perceived exertion (RPE) as an index of aerobic endurance during local and general exercises.

The main purpose of this study was to assess the correlations of RPE with indicators of endurance (critical power), exhaustion time and the electromyographic activity of a relevant muscle during general and local exercises. Eight healthy subjects participated in the study. During the first session, Maximal Aerobic Power (MAP) was measured by means of an incremental cycling exercise on a Monark ergometer. At 1-week intervals the participants performed a general or local exhausting exercise, which consisted of a cycle exercise (60, 73, 86 or 100% MAP) and a knee extension exercise (lifting a load between 17.5 and 32.5 kg every 3 s), respectively. The critical powers corresponding to cycling (CPcycling) and knee extension (CPknee) were calculated from the slope of the linear relationship between exhaustion time (tlim) and work. Rate of perceived exertion, concerning the whole body (overall RPE [RPEov]), RPE concerning the exercising muscles (muscular RPE [RPEmu]) and exhaustion time were measured. During the last session, the integrated electromyogram of the right Vastus Lateralis (iEMG s-1) was measured during short (20 s) cycling and knee extension non-exhausting exercises, with the same electrode location, at the different power outputs used during the exhausting exercises. The relationships between RPEmu at the fifth minute and log tlim and between iEMG% (percentage of the iEMG s-1 corresponding to 100% MAP during cycling) and log tlim were similar for the cycling and knee extension exercises. The mean values of RPEmu at the fifth minute of exercise calculated for CPcycling and CPknee were almost equal (12.3 +/- 1.7 versus 12.2 +/- 0.9). Similarly, the mean values of iEMG% corresponding to CPcycling and CPknee were equal (78.44 versus 79.02%). These results suggest that RPEmu is related to aerobic endurance and that the possibility of sustaining a high percentage of maximal aerobic power during a general exercise is mainly related to local muscular factors.

Maximal power and force-velocity relationships during cycling and cranking exercises in volleyball players. Correlation with the vertical jump test.

BACKGROUND: The aim of this study was to propose a test battery adjusted to volleyball players and to study the links between dynamic (vertical jump, force-velocity relationships and maximal anaerobic power in cranking and cycling) and static (maximal voluntary force and rate of force development in isometric conditions) performances. METHODS: The relationships between braking force (F) and peak velocity (V) have been determined for cycling and cranking exercises in 18 male volleyball players of a district league. According to previous studies, these F-V relationships were assumed to be linear and were expressed as follows: V = V0(1-F/F0), where V0 should be an estimate of the maximal velocity at zero braking force whereas F0 is assumed to be a braking force corresponding to zero velocity. Maximal anaerobic power in cycling (Pmax leg) and cranking (Pmax arm) were calculated as equal to 0.25 V0F0. The same subjects performed a vertical jump test (VJ) and a strength test on an isometric leg press with the measurement of the unilateral isometric maximal voluntary force (MVF) and indices of rate of isometric force development (RFD): maximal rate of force development (MRFD) and the time from 25% to 50% of MVF (T25-50). RESULTS: Pmax leg (15.8 +/- 1.4 W.kg-1) and V0 arm (259.6 +/- 13.1 rpm) were high but similar to the results of elite athletes, previously collected with the same protocols and the same devices. VJ was significantly with F0 leg, Pmax leg and Pmax arm related to body mass. The performances of the dynamic tests were significantly correlated and especially the parameters (V0, F0, Pmax) of the force velocity tests in cycling were significantly correlated with the same parameters in cranking. The results of the isometric tests (MVF, MRFD) were not correlated with VJ, except T25-50 of the left leg. CONCLUSIONS: A vertical jump test and a force velocity test with the arms are proposed for a test battery in volleyball players.

Work-exhaustion time relationships and the critical power concept. A critical review.

The present review is focused on the physiological meanings of the critical power concept proposed by Scherrer in 1954 and its applications to general exercises such as running, cycling and swimming. Since the first studies on the critical power of local exercises, many studies have found that critical power is correlated with indices which are related to aerobic endurance such as maximal oxygen uptake, ventilatory threshold, OBLA or maximal lactate steady state. In fact, the relationship between exhaustion time t(lim) and the Work Wlim (or Distance Dlim) performed at exhaustion is not exactly linear and, consequently, the power-t(lim) equation is not a true hyperbola. The effect of the range of t(lim), used in the calculation of the slope of the Wlim-t(lim) relationship (called critical power) are discussed. When critical power is calculated from short supramaximal exercises, this power is higher than the power output which corresponds to a lactate steady state (or an oxygen uptake steady state) and does not correspond to a power output which can be sustained a long time. The authors present experimental data collected during local (knee extension) and general (running and cycling) exercises which suggest that critical power could correspond to a steady state provided that critical power is calculated from heavy submaximal exercises only (t(lim) ranging between 6 and 30 min). It is difficult to predict exhaustion time from critical power or critical velocity because of the hyperbolic nature of the power-t(lim) relationship. On the other hand, a large error in the measure of t(lim) should have a small effect on the calculation of critical power or velocity. In contrast, the value of Y intercept of the Wlim-t(lim) (or Dlim-(t(lim)) relationship should be sensitive to errors in t(lim).

Effects of aerobic exercise on the torque-velocity relationship in cycling.

The kinetics of the torque-velocity (T-omega) relationship after aerobic exercise was studied to assess the effect of fatigue on the contractile properties of muscle. A group of 13 subjects exercised until fatigued on a cycle ergometer, at an intensity which corresponded to 60% of their maximal aerobic power for 50 min (MAP60%); ten subjects exercised until fatigued at 80% of their maximal aerobic power for 15 min (MAP80%). Of the subjects 7 exercised at both intensities with at least a 1-week interval between sessions. Pedalling rate was set at 60 rpm. The T-omega relationship was determined from the velocity data collected during all-out sprints against a 19 N.m braking torque on the same ergometer, according to a method proposed previously. Maximal theoretical velocity (omega zero) and maximal theoretical torque (Tzero) were estimated by extrapolation of the linear T-omega relationship. Maximal power (Pmax) was calculated from the values of Tzero and omega zero (Pmax = 0.25 omega zero Tzero). The T-omega relationships were determined before, immediately after and 5 and 10 min after the aerobic exercise. The kinetics of omega zero, Tzero and Pmax was assumed to express the effects of fatigue on the muscle contractile properties (maximal shortening velocity, maximal muscle strength and maximal power). Immediately after exercise at MAP60% a 7.8% decrease in Tzero and 8.8% decrease in Pmax was seen while the decrease in omega zero was nonsignificant, which suggested that Pmax decreased in the main because of a loss in maximal muscle strength. In contrast, MAP80% induced a 8.1% decrease in omega zero and 12.8% decrease in Pmax while the decrease in Tzero was nonsignificant, which suggested that the main cause of the decrease in Pmax was probably a slowing of maximal shortening velocity. The short recovery time of the T-omega relationship suggests that the causes of the decrease of torque and velocity are processes which recover rapidly.

Torque-velocity relationship during cycle ergometer sprints with and without toe clips.

The torque-velocity relationship in cycling has been studied during all-out sprints (n = 6 subjects) with and without toe clips on an electronic Lode ergometer with strain gauges, to estimate the importance of the expected decrease in torque, velocity and power output. As previously found with different cycling protocols, the torque-velocity relationship was linear for all-out sprints with toe clips. A similar relationship was observed when cycling without toe clips but the torque-velocity relationship was inflected downwards at low or high velocities in several subjects who were not regular cyclists. The pulling action during the rise of the pedal at low velocities cannot explain why the torque-velocity relationship is not hyperbolic for cycling exercises with toe clips because similar relationships were observed without toe clips. The maximal power output was significantly higher during cycling with toe clips (782 W vs 668 W, P < 0.05), probably because of the pulling action at low and medium velocities as indicated by the higher value of the extrapolated maximal torque T0 (138 N x m vs 122 N x m, P < 0.05). In contrast, the maximal extrapolated velocity, V0 and peak velocity were not significantly improved by the use of toe clips. The comparison of the angle-torque patterns at low and high velocities suggested that the kinetic energy of the legs can be transformed into power output when cycling without toe clips as well as it can when cycling with toe clips.

Relationship between maximal oxygen uptake on different ergometers, lean arm volume and strength in paraplegic subjects.

The present experiment was designed to study the importance of strength and muscle mass as factors limiting maximal oxygen uptake (VO2max) in wheelchair subjects. Thirteen paraplegic subjects [mean age 29.8 (8.7) years] were studied during continuous incremental exercises until exhaustion on an arm-cranking ergometer (AC), a wheelchair ergometer (WE) and motor-driven treadmill (TM). Lean arm volume (LAV) was estimated using an anthropometric method based upon the measurement of various circumferences of the arm and forearm. Maximal strength (MVF) was measured while pushing on the rim of the wheelchair for three positions of the hand on the rim (-30 degrees, 0 degrees and +30 degrees). The results indicate that paraplegic subjects reached a similar VO2max [1.23 (0.34) 1 x min(-1), 1.25 (0.38) 1 x min(-1), 1.22 (0.18) 1 x min(-1) for AC, TM and WE, respectively] and VO2max/body mass [19.7 (5.2) ml x min(-1) x kg(-1), 19.5 (6.14) ml x min(-1) x kg(-1), 19.18 (4.27) ml x min(-1) x kg(-1) for AC, TM and WE, respectively on the three ergometers. Maximal heart rate f((c) (max)) during the last minute of AC (173 (17) beats x min(-1)], TM [168 (14) beats x min(-1)], and WE [165 (16) beats x min(-1)], were correlated, but f((c) (max)) was significantly higher for AC than for TM (P < 0.03). There were significant correlations between MVF and LAV (P < 0.001) and between the MVF data obtained at different angles of the hand on the rim [311.9 (90.1) N, 313.2 (81.2) N, 257.1 (71) N, at -30 degrees, 0 degrees and +30 degrees, respectively]. There was no correlation between VO2max and LAV or MVF. The relatively low values of f((c) (max)) suggest that VO2max was, at least in part, limited by local aerobic factors instead of central cardiovascular factors. On the other hand, the lack of a significant correlation between VO2max and MVF or muscle mass was not in favour of muscle strength being the main factor limiting VO2max in our subjects.