Differences in mechanical efficiency between power- and endurance-trained athletes while jumping

Mechanical efficiency (ME) of jumping exercises was compared between power-trained (n = 11) and endurance-trained athletes (n = 10) using both a biomechanical and a physiological approach. In drop jumps and in stretch-shortening cycle exercise on a special sledge (sledge jumps), the subjects performed 60 muscle actions from a dropping height of optimum minus 40 cm (O – 40), as well as from dropping heights of optimum (O) and optimum plus 40 cm (O + 40). Thus, they were tested in six different tests which lasted for a total of 3 min for each. The mean ME values in the drop jumps from the lowest dropping height upwards were as follows: 23.8 (SD 5.3)%, 35.5 (SD 10.8)% and 39.2 (SD 6.6)% for the power group, and 30.8 (SD 6.5)%, 37.5 (SD 8.7)% and 41.4 (SD 7.0)% for the endurance group. In the sledge jumps the ME values were 37.0 (SD 5.6)%,48.4 (SD 4.0)% and 54.9 (SD 8.5)% for the power group, and 40.2 (SD 5.9)%, 46.9 (SD 5.7)% and 58.5 (SD 5.5)% for the endurance group. As can be seen, the ME values increased with increasing stretch load. However, the groups did not differ from each other except in the drop jump condition of O – 40 (P < 0.05). The higher power (P < 0.001) among the power athletes in every measured condition was associated with a faster rate of electromyogram development during the pre-activity, and smoother muscle activity patterns in the ground contact. On the other hand, the endurance athletes had a lower blood lactate concentration after every test, and in addition a lower heart rate and ventilation during the sledge jumps than their power counterparts. Therefore, it would seem that the similar mean ME values between the subject groups could be explained by improved function of the neuromuscular system among the power group and improved metabolism among the endurance group.     

Force-, EMG-, and elasticity-velocity relationships at submaximal,maximal and supramaximal running speeds in sprinters

Summary The relationships between ground reaction forces, electromyographic activity (EMG), elasticity and running velocity were investigated at five speeds from submaximal to supramaximal levels in 11 male and 8 female sprinters. Supramaximal running was performed by a towing system. Reaction forces were measured on a force platform. EMGs were recorded telemetrically with surface electrodes from the vastus lateralis and gastrocnemius muscles, and elasticity of the contact leg was evaluated with spring constant values measured by film analysis. Data showed increases in most of the parameters studied with increasing running speed. At supramaximal velocity (10.36±0.31 m×s⁻¹; 108.4±3.8%) the relative increase in running velocity correlated significantly (P<0.01) with the relative increase in stride rate of all subjects. In male subjects the relative change in stride rate correlated with the relative change of IEMG in the eccentric phase (P<0.05) between maximal and supramaximal runs. Running with the towing system caused a decrease in elasticity during the impact phase but this was significant (P<0.05) only in the female sprinters. The average net resultant force in the eccentric and concentric phases correlated significantly (P<0.05−0.001) with running velocity and stride length in the maximal run. It is concluded that (1) increased neural activation in supramaximal effort positively affects stride rate and that (2) average net resultant force as a specific force indicator is primarily related to stride length and that (3) the values in this indicator may explain the difference in running velocity between men and women.     

Mechanical power and segmental contribution to force impulses in long jump take-off

Summary Changes in total mechanical work, its partitioning into different energy states, mechanical power, force-time characteristics, force impulses of body segments and mass center's pathway characteristics during long jump take-off were investigated on four national and six ordinary level athletes. Both cinematographic and force-platform techniques were used. The data showed that the national level jumpers had higher run-up and higher take-off (release) velocities in horizontal and vertical directions. In addition, they were able to utilize efficiently the elastic energy stored in the leg extensor muscles at take-off impact. This was seen in high support leg eccentric and concentric forces, which were produced in short contact times. The ordinary level athletes had greater variability in the investigated attributes, and they reached their maximum length of jumps in many different ways. Cinematically the greatest difference between the subject groups was observed in the timing of the various body segment movements. In better athletes all the body parts (arms, trunk, and legs) had decelerating horizontal impulses, but in all ordinary level athletes the horizontal impulse of the swing leg was accelerating during take-off.     

Adaptational phenomena and mechanical responses during running: effect of surface, aging and task experience

The goals of the study were to identify adaptational phenomena in running mechanics over a variety of surfaces due to age related changes in the muscle-tendon units (MTUs) capacities, to examine whether running experience is associated with adaptational effects on running mechanics over a variety of surfaces even at old age, and to investigate whether surface condition affects running mechanics. The investigation was executed on 30 old and 19 young including 29 runners and 20 non-active subjects. In a previous study we documented that the older had lower MTUs capacities. In the present study running mechanics were analysed as the same subjects ran at 2.7 m/s over three surfaces having different compliance. Surface condition did not affect centre of mass trajectory, duty factor or joint kinetics (P > 0.01). Older react to the reduced MTUs capacity by increasing duty factor and benefiting from a mechanical advantage for the triceps surae MTU and a lower rate of force generation on all surfaces (P < 0.01). Runners displayed lower average horizontal forces and a higher mechanical advantage for the quadriceps femoris MTU for all surfaces (P < 0.01). The results provided strong evidence on that running strategy remained essentially unchanged over a variety of surfaces. Adaptive improvements in running mechanics due to task experience were present for all surfaces and did not depend on age. We further concluded that older adults were able to recalibrate their running strategy to adjust the task effort to the reduced MTUs capacities in a feedforward control manner for a variety of mechanical environments.     

Mechanical energy states during running

Summary Changes in total mechanical work and its partitioning into different energy states (kinetic, potential and rotational) during a step cycle of running were investigated on six well trained athletes who ran at the test speeds of 40, 60, 80, and 100% (9.3±0.3 m/s) of maximum. Cinematographic techniques were utilized to calculate the mechanical energy states as described by Norman et al. (1976), using a 13 segment mechanical model of a runner as the basis for the computations. The data showed that both the kinetic and rotational energy increased parabolically but the potential energy decreased linearly with increases in running velocity. The calculated power of the positive work phase increased quadratically with running speed. During the phase when the runner was in contact with the ground, the applied calculations gave similar increases for the positive and negative works, and the power ratio (W _neg/W _pos) stayed the same at all measured speeds. Therefore, it is likely that the method used to calculate the various mechanical energy states did not reflect accurately enough the physiological energy costs at higher running speeds. It may, however, be quite acceptable for estimating the mechanical energy states during walking and slow running, in which case the role of negative work is less and consequently the storage and utilization of elastic energy is small.     

Mechanics of human triceps surae muscle in walking, running and jumping

Length changes of the muscle-tendon complex (MTC) during activity are in part the result of length changes of the active muscle fibres, the contractile component (CC), and also in part the result of stretch of elastic structures [series-elastic component (SEC)]. We used a force platform and kinematic measurements to determine force and length of the human calf muscle during walking, running and squat jumping. The force-length relation of the SEC was determined in dynamometer experiments on the same four subjects. Length of the CC was calculated as total muscle-tendon length minus the force dependent length of the SEC. The measured relations between force and length or velocity were compared with the individually determined force-length and force-velocity relations of the CC. In walking or running the negative work performed in the eccentric phase was completely stored as elastic energy. This elastic energy was released in the concentric phase, at speeds well exceeding the maximum shortening speed predicted by the Hill force-velocity relation. Speed of the CC, in contrast, was positive and low, well within the range predicted by the measured force-velocity properties and compatible with a favourable muscular efficiency. These effects were also present in purely concentric contractions, like the squatted jump. Contractile component length usually started at the far end of the force-length relation. Inter-individual differences in series-elastic stiffness were reflected in the force and length recordings during natural activity.     

Mechanical power during maximal treadmill walking and running in young and elderly men

This study determined mechanical power during movements specific to maximal walking and running using a non-motorized treadmill in 38 elderly [69.4 (5.0) years] and 50 young [24.3 (3.4) years] men. The mean mechanical power over a period of time covering six steps, during which the belt velocity peaked and then kept almost plateau, was determined as a performance score in each of maximal walking (WP) and running (RP). In terms of the value relative to body mass, the relative difference between the two age groups was greater for RP (61.7%) than for WP (21.4%) or isometric knee extension (34.1%) and flexion torque (43.8%). In the two groups, WP was significantly (P<0.05) correlated to knee extension (r=0.582 for the elderly and r=0.392 for the young) and flexion torque (r=0.524 for the elderly and r=0.574 for the young). Similarly, RP was also significantly (P<0.05) correlated to knee extension (r=0.627 for the elderly and r=0.478 for the young) and flexion torque (r=0.500 for the elderly and r=0.281 for the young). In these relationships, the WP adjusted statistically by thigh muscle torque was similar in the two age groups. However, the corresponding value for RP was significantly higher in the young than in the elderly. The findings here indicate that: (1) the difference between the young and elderly men in mechanical power is greater during maximal running than maximal walking, and (2) although the thigh muscle torque contributes to the power production during the two maximal exercise modes in the two age groups, the RP is greater in the young than in the elderly regardless of the difference in the thigh muscle torque.     

Energy expenditure and cardiorespiratory responses at the transition between walking and running

We investigated whether the spontaneous transition between walking and running during moving with increasing speed corresponds to the speed at which walking becomes less economical than running. Seven active male subjects [mean age, 23.7 (SEM 0.7) years, mean maximal oxygen uptake ( ), 57.5 (SEM 3.3) ml·kg ^–1·min ^–1, mean ventilatory threshold (VTh), 37.5 (SEM 3) ml·kg ^–1 ·min ^–1] participated in this study. Each subject performed four exercise tests separated by 1-week intervals: test 1, and VTh were determined; test 2, the speed at which the transition between walking and running spontaneously occurs (ST) during increasing speed (increases of 0.5 km·h ^–1 every 4 min from 5 km·h ^–1) was determined; test 3, the subjects were constrained to walk for 4 min at ST, at ST ± 0.5 km·h ^–1 and at ST ± 1 km·h ^–1; and test 4, the subjects were constrained to run for 4 min at ST, at ST±0.5 km·-h ^–1 and at ST±1 km·h ^–1. During exercise, oxygen uptake ( ), heart rate (HR), ventilation ( ), ventilatory equivalents for oxygen and carbon dioxide (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmOvayaaca% WaaSbaaSqaaiaabweaaeqaaOGaai4laiqadAfagaGaamaaBaaaleaa% caqGYaaabeaakiaacYcacaqGGaGaaeiiaiqadAfagaGaamaaBaaale% aacaqGfbaabeaakiaac+caceWGwbGbaiaacaqGdbGaae4tamaaBaaa% leaacaaIYaaabeaaaaa!4240!\[\dot V_{\text{E}} /\dot V_{\text{2}} ,{\text{ }}\dot V_{\text{E}} /\dot V{\text{CO}}_2 \]), respiratory exchange ratio (R), stride length (SL), and stride frequency (SF) were measured. The results showed that: ST occurred at 2.16 (SEM 0.04) m·s ^–1; , HR and speed at ST were significantly lower than the values measured at VTh (P< 0.001, P< 0.001 and P< 0.05, respectively); changed significantly with speed (P< 0.001) but was greater during running than walking below ST (ST minus 1 km·h ^–1, P< 0.001; ST minus 0.5 km·h ^–1, P< 0.05) with the converse above ST (ST.plus 1 km·h ^–1, P<0.05), whereas at ST the values of were very close [23.9 (SEM 1.1) vs 23.7 (SEM 0.8) ml·kg ^–1 · min ^–1 not significant, respectively, for walking and running]; SL was significantly greater during walking than running (P<0.001) and SF lower (P<0.001); and HR and were significantly greater during running than walking below ST (ST minus 1 km·h ^–1, P<0.01; ST minus 0.5 km·h ^–1, P{<0.05) with the converse above ST (ST plus 1 km·h ^–1, P·< 0.05), whereas no difference appeared for and R between the two types of locomotion. We concluded from this study that ST corresponded to the speed at which the energy expenditure of running became lower than the energy expenditure of walking but that the mechanism of the link needed further investigation.     

The energy cost of walking and running with and without a backpack load

Summary The effect of a backpack load (20 kg) on oxygen consumption while walking and running at different speeds was investigated. Fifteen males walked and ran (with and without load) up a 5% sloped treadmill at 6.4, 7.2, 8.0, 9.6, and 11.2 km/h (4, 4.5, 5, 6, and 7 mph). While walking O₂ rose at a rate of 0.6 (l/min)/(km/h) and while running 0.3 (l/min)/(km/h). The mean oxygen consumption at the various speeds was 28.65, 33.78, 40.64, 46.84, 54.48 ml O₂/kg BW/min, respectively, for the whole group without load and 26.52, 32.26, 38.28, 44.26, 48.16, respectively, with load. The breaking point between walking and running was at about 8.2 km/h. Carrying the load increased O₂ at a constant rate, and induced a breaking point between walking and running at a significantly lower speed for the smaller subjects than for the more robust ones. The results indicate that for certain tasks involving endurance and heavy load carriage, people should be selected according to criteria which integrate aerobic capacity and anthropometrical features.     

A comparison of resistance and aerobic training for mass, strength and turnover of bone in growing rats

To determine the effects of resistance versus aerobic exercise on the mass, strength and turnover of bone, thirty Sprague Dawley rats (4 weeks of age) were assigned to one of three experimental groups: sedentary, running or jumping. In the jumping group, the trunk was kept upright during electrically stimulated jumping exercise for 1 h every other day. The running rats ran at speeds of 24 m/min for 1 h every other day. After 4 weeks, the jumping rats exhibited increases in the mass and strength of the lumbar vertebrae and of the mid-diaphysis of the femur (mid-femur), and increases in the cross-sectional morphology of these bones: the trabecular bone volume per bone surface, the trabecular thickness, the trabecular bone formation rate per bone surface (BFR/BS). In addition, they exhibited reduced trabecular separation and the area of osteoclast surface per bone surface. The running and sedentary rats showed no such changes. With regard to the mid-femur, in both the jumping and running rats the periosteal BFR/BS was increased. However, only the jumping rats showed a reduction in the BFR/BS at the endocortical surface. These results suggest that resistance exercise accelerates cortical drift and increases the bone mass and strength by stimulating bone formation more efficiently than does aerobic exercise. Accepted: 9 August 2000     

Ratings of perceived exertion in individuals with varying fitness levels during walking and running

Summary It was the purpose of this investigation to: 1) compare the ratings of perceived exertion (RPEs) in high and low fit individuals when walking and running at comparable exercise intensities and 2) to determine if ventilation provides a central signal for RPEs. Nine high fit and nine low fit male subjects completed two exercise bouts on a treadmill, one uphill walking and the other level running. Workloads for each bout were set at 90% of each subject's ventilatory threshold (VT) as determined from a graded exercise test. Oxygen consumption heart rate (HR), and were all similar between the walk and run trials for the low fit subjects (P>0.05). HR were found to be significantly greater during the walk trial vs. the run trial (P<0.05) for the high fit subjects, whereas, was significantly greater during the run trial. Oxygen consumption was similar for the high fit subjects during both trials (P>0.05). During the walk and run trials, central (12.1±.6 vs. 11.4±1.5), local (14.0±1.3 vs. 13.9+1.1) and overall (12.8±1.2 vs. 12.4±1.4) RPEs were not found to be significantly different for the low fit group (P>0.05). In contrast, during the walk vs. the run trial there was a significant increase in central (10.7±2.0 vs. 9.2±1.9), local (11.5±2.0 vs. 9.8±1.8) and overall (11.2±2.4 vs. 9.6±2.3) RPEs for the high fit group (P<0.05). There were significant differences (P<0.05) when comparing local, central and overall RPEs during both the walk and run trials for the low fit group with local RPEs being significantly greater than both central and overall RPEs. There was no significant difference (P>0.05) between central and overall RPEs in either the walk or run trial for the low fit group. No significant differences (P> 0.05) were found between the central, local and overall RPEs for either the walk or run trial with the high fit group. Based on the above results, it appears as if walking is perceptually more stressful than running at similar exercise intensities for high fit individuals. Since was greater for the run trial vs. the walk trial for the high fit subjects, yet RPEs were lower, it does not appear as if provides a central signal for the determination of RPEs.     

Can cycle power predict sprint running performance?

Summary A major criticism of present models of the energetics and mechanics of sprint running concerns the application of estimates of parameters which seem to be adapted from measurements of running during actual competitions. This study presents a model which does not perpetuate this solecism. Using data obtained during supra-maximal cycle ergometer tests of highly trained athletes, the kinetics of the anaerobic and aerobic pathways were modelled. Internal power wasted in the acceleration and deceleration of body limbs and the power necessary to overcome air friction was calculated from data in the literature. Assuming a mechanical efficiency as found during submaximal cycling, a power equation was constructed which also included the power necessary to accelerate the body at the start of movement. The differential equation thus obtained was solved through simulation. The model appeared to predict realistic times at 100 m (10.47 s), 200 m (19.63 s) and 400 m (42.99 s) distances. By comparison with other methods it is argued that power equations of locomotion should include the concept of mechanical efficiency.     

Relationship between the efficiency of muscular work during jumping and the energetics of running

Summary The running economy of seventeen athletes was studied during running at a low speed (3.3 m · s^–1) on a motor-driven treadmill. The net energetic cost during running expressed in kJ·kg^–1·km^–1 was on average 4.06. As expected, a positive relationship was found between the energetic cost and the percentage of fast twitch fibres (r=0.60,n=17,p<0.01). In addition, the mechanical efficiency during two different series of jumps performed with and without prestretch was measured in thirteen subjects. The effect of prestretch on muscle economy was represented by the ratio between the efficiency of muscular work performed during prestretch jumps and the corresponding value calculated in no prestretch conditions. This ratio demonstrated a statistically significant relationship with energy expenditure during running (r=–0.66,n=13,P<0.01), suggesting that the elastic behaviour of leg extensor muscles is similar in running and jumping if the speeds of muscular contraction during eccentric and concentric work are of similar magnitudes.     

Acute changes in muscle activation and leg extension performance after different running exercises in elite long distance runners

This study investigated acute changes in muscle activation and muscular power performance after three different running exercises in elite long-distance runners. Twenty-two nationally and internationally ranked long-distance runners performed first an incremental treadmill running test until exhaustion (MR) and then 40 min continuous (TR) and intermittent (2 min run/2 min rest) (IR) running exercises at an intensity of 80 and 100% of the velocity associated with VO_2max, respectively. Muscle activation and muscular power performance tests (counter-movement jumps, CMJ, and a set of ten maximal half squats from the static starting position with an extra load of 35% of the subjects,′ one repetition maximum) were performed before and immediately after the runs. The average mechanical power (P) of the half squats was calculated and the root mean square electromyogram (EMGrms) from the vastus lateralis, vastus medialis, gastrocnemius and biceps femoris muscles was recorded simultaneously during the half squat performances. The results showed an acute exercise–induced increase in P (ANOVA time effect, P=0.000) together with a reduction in EMGrms of the knee extensor muscles (ANOVA time effect, P=0.000). However, mechanical P expressed as a relative change within the set decreased after MR. In TR the improvement in P correlated positively with the maximal running performance of the runners (P<0.05), while in IR it correlated negatively (P<0.05). Jumping performance was significantly enhanced after each run (P<0.001, for all) and the improvement correlated negatively with the maximal sprinting speed and maximal jumping height of the runners (P<0.01, for all). It is concluded that in elite long distance runners an intensive prolonged running exercise reduces the surface EMG of the knee extensor muscles, and may lead to a different coordination strategy in leg extension exercises performed into the vertical direction. After continuous type of running the power improvement correlates positively with maximal endurance running capacity, whereas after intermittent type of running it correlates negatively.     

Influence of 2D and 3D body segment models on energy calculations during kinematic analysis of running

The aims of the present study were: (1) to examine the influence of two-dimensional (2D) and three-dimensional (3D) analysis on the body's total energy during the support phase of running, and (2) to examine the influence of the choice of anthropometric models on the body's total energy during running. A total of 14 runners participated in the investigation [mean (SD) height: 1.83 (0.03) m, body mass: 79.67 (5.65) kg]. Two genlocked high-speed cameras (120 Hz) filmed each athlete's movement during single-foot ground contact. The exact support time of the athletes was measured with a Kistler force plate (sampling frequency: 1000 Hz). The masses and moments of inertia of the various segments were estimated using the 2D and 3D models of Hanavan (1964) as well as the 3D model of Zatsiorsky et al. (1984).The influence of the 2D and 3D analysis on the calculations was evaluated by comparing of the total energies calculated using Hanavan's 2D and 3D models. The influence of the choice of the anthropometric model on the calculations was checked by comparing the results obtained using the Hanavan 3D model and those obtained using the 3D model of Zatsiorsky et al. (1984). The data show us that 2D and 3D analyses produce similar energy values during the entire support phase of running (only very small percentage energy differences were observed: e.g. from 0.23% for the energy of the body at the first contact with the ground, up to 0.31% for the energy of the body at the time the athlete leaves the ground, E _TO). In addition, calculations made using the 3D models of Hanavan and Zatsiorsky also produced similar results for energy values (energy differences from 0.33% for energy minimum, up to 0.8% for E _TO). It can be assumed, therefore, that neither the choice of the anthropometric model nor the calculations made on the basis of 3D coordinates are limiting factors in the calculation of body total energies for running. Electronic Publication     

Maximal oxygen uptake,anaerobic threshold and running economy in women and men with similar performances level in marathons

Sex differences in running economy (gross oxygen cost of running, C_R), maximal oxygen uptake (VO_2max), anaerobic threshold (Th_an), percentage utilization of aerobic power (% VO_2max), and Th_an during running were investigated. There were six men and six women aged 20–30 years with a performance time of 2 h 40 min over the marathon distance. The VO_2max, Th_an, and CR were measured during controlled running on a treadmill at 1° and 3° gradient. From each subject's recorded time of running in the marathon, the average speed (v _M) was calculated and maintained during the treadmill running for 11 min. The VO_{2 max} was inversely related to body mass (m _b), there were no sex differences, and the mean values of the reduced exponent were 0.65 for women and 0.81 for men. These results indicate that for running the unit ml·kg^–0.75·min^–1 is convenient when comparing individuals with different m _b. The VO_2max was about 10% (23 ml·kg^–0.75·min^–1) higher in the men than in the women. The women had on the average 10–12 ml·kg^–0.75·min^–1 lower VO₂ than the men when running at comparable velocities. Disregarding sex, the mean value of C_R was 0.211 (SEM 0.005) ml·kg^–1·m^–1 (resting included), and was independent of treadmill speed. No sex differences in Th_an expressed as % VO_2max or percentage maximal heart rate were found, but Than expressed as VO₂ in ml·kg^–0.75·min^–1 was significantly higher in the men compared to the women. The percentage utilization of f _emax and concentration of blood lactate at v _M was higher for the female runners. The women ran 2 days more each week than the men over the first 4 months during the half year preceding the marathon race. It was concluded that the higher VO_2max and Th_an in the men was compensated for by more running, superior C_R, and a higher exercise intensity during the race in the performance-matched female marathon runners.     

Comparison of the clinical features of suicide attempters by jumping from a height and those by self-stabbing in Japan

Background

A history of psychiatric disorders is a high risk for suicide. The present study compared the clinical features of psychiatric patients in Japan who attempted suicide by jumping from a height and those who attempted suicide by self-stabbing.

Methods

We compared two groups of suicide attempters who were hospitalized for both physical and psychiatric treatment (n=202). We compared the psychiatric diagnoses and clinical features between those who attempted suicide by jumping from a height (N=147) and those who did so by self-stabbing (N=55).

Results

The self-stabbing group (mean age 52.3 years) was significantly older compared to the jumping group (mean age 37.9 years). A significantly higher proportion of females were found in the jumping group. Jumping from a height was significantly associated with schizophrenia spectrum disorders, whereas self-stabbing was significantly associated with mood disorders.

Limitations

The results were drawn from data from a single hospital in a large urban city, and the study population did not include subjects who completed their suicide attempts.

Conclusions

Our findings show that differences in suicide methods (here, between jumping from a height and self-stabbing) may be related to suicide attempters' psychiatric diagnosis, gender and age. It is thus important to obtain a more detailed background information about a patient's suicide attempt and to create suicide prevention plans in accord with individuals' psychiatric diagnosis, age and gender, especially among those who have attempted suicide by jumping from a height or self-stabbing.     

Ergometry for estimation of mechanical power output in sprinting in humans using a newly developed self-driven treadmill

An evaluation of mechanical power during walking and running in humans was undertaken after developing a specially designed running ergometer (RE) in which the subjects gripped the handlebar in front of them keeping both arms straight and in a horizontal position. Ten subjects participated in comparisons of the mean horizontal pushing force (MF _am) on the handlebar with the mean horizontal ground reaction force (MF _fp) recorded by force platform under the RE during five different constant speeds of walking or running and sprint running with maximal effort. Mechanical power developed during sprint running on the RE was compared with a 50 m sprint. Mean linear velocity (Mv) of the RE belt was recorded by the rotary encoder attached to the axis of the belt. Mean mechanical power calculated from the handlebar setting (MP _am=MF _am × Mv) was compared to that calculated from force platform recordings (MP _fp=MF _fp × Mv). A high test-retest reproducibility was observed for both MF _fp (r=0.889) and MF _am (r=0.783). Larger values for the coefficient of variation for MF _am (11.3%–15.8%) were observed than for MF _fp (3.3%–8.2%). The MP _am, which were obtained from five different constant speeds of walking, running and sprint running were closely correlated to those of MP _fp (y=0.98x − 19.10,r=0.982, P < 0.001). In sprint running, MP _am was 521.7 W (7.67 W · kg⁻¹) and was correlated to the 50 m sprint time (r=−0.683, P < 0.01). It is concluded that the newly developed RE was useful in the estimation of mechanical power output during human locomotion such as when walking, jogging and sprinting. Accepted: 10 October 2000     

Oxygen kinetics and modelling of time to exhaustion whilst running at various velocities at maximal oxygen uptake

The purpose of this study was to characterise the relationship between running velocity and the time for which a subject can run at maximal oxygen uptake (V˙O_{2 max}), (t _lim V˙O_{2 max}). Seven physical education students ran in an incremental test (3-min stages) to determine V˙O_{2 max} and the minimal velocity at which it was elicited (νV˙O_{2 max}). They then performed four all-out running tests on a 200-m indoor track every 2 days in random order. The mean times to exhaustion t _lim at 90%, 100%, 120% and 140% νV˙O_{2 max} were 13 min 22 s (SD 4 min 30 s), 5 min 47 s (SD 1 min 50 s), 2 min 11 s (SD 38 s) and 1 min 12 s (SD 18 s), respectively. Five subjects did not reach V˙O_{2 max} in the 90% νV˙O_{2 max} test. All the subjects reached V˙O_{2 max} in the runs at 100% νV˙O_{2 max}. All the subjects, except one, reached V˙O_{2 max} in the runs at 120%νV˙O_{2 max}. Four subjects did not reach V˙O_{2 max} in the 140% νV˙O_{2 max} test. Time to achieve V˙O_{2 max} was always about 50% of the time to exhaustion irrespective of the intensity. The time to exhaustion-velocity relationship was better fitted by a 3- than by a 2-parameter critical power model for running at 90%, 100%, 120%, 140% νV˙O_{2 max} as determined in the previous incremental test. In conclusion, t _lim V˙O_{2 max} depended on a balance between the time to attain V˙O_{2 max} and the time to exhaustion t _lim. The time to reach V˙O_{2 max} decreased as velocity increased. The t _lim V˙O_{2 max} was a bi-phasic function of velocity, with a peak at 100% νV˙O_{2 max}. Accepted: 2 February 2000