Faster top running speeds are achieved with greater ground forces not more rapid leg movements

The effect of different first 200-m pacing strategies on blood lactate and biomechanical parameters of the 400-m sprint

The purpose of the present study was to evaluate the effect of three pacing strategies upon performance of the 400-m sprint. Eight healthy male physical education students participated in this study. Each participant performed a 200-m maximal test (200(MAX)) and three 400-m running tests in a random counterbalanced design. The 400-m tests were run with the first 200-m pace set at 98% (400(98%)), 95% (400(95%)), and 93% (400(93%)), respectively, of the effort for 200(MAX). The stimulation of the lactate system was assessed by post-test blood lactate concentration (BLa). Running speed (RS) was controlled with time-keeping devices. Stride frequency (SF), stride length (SL) and lower extremity kinematics were acquired with video cameras operating at 100 fps at the 125 and 380-m marks of the tests. A two-way analysis of variance (ANOVA) with repeated measures was used to identify modifications caused by the pacing strategies used. Non-significant differences were revealed for BLa. The fastest 400-m race was run in 400(93%), but performance was not significantly different (p > 0.05) among the examined pacing strategies. RS, SF and SL had significantly (p < 0.05) lower values in the 380-m mark when compared with the 125-m mark. In 400(98%), both SF and SL decreased by approximately 13%, while SF and SL dropped 2.4 and 9.2%, respectively, in 400(93%). In conclusion, lower peak BLa and less unfavorable modifications of running mechanics were recorded in 400(93%), where time differential between the halves of the 400-m race was smaller, which eventually resulted in better performance.

Grip and limb force limits to turning performance in competition horses

Manoeuverability is a key requirement for successful terrestrial locomotion, especially on variable terrain, and is a deciding factor in predator-prey interaction. Compared with straight-line running, bend running requires additional leg force to generate centripetal acceleration. In humans, this results in a reduction in maximum speed during bend running and a published model assuming maximum limb force as a constraint accurately predicts how much a sprinter must slow down on a bend given his maximum straight-line speed. In contrast, greyhounds do not slow down or change stride parameters during bend running, which suggests that their limbs can apply the additional force for this manoeuvre. We collected horizontal speed and angular velocity of heading of horses while they turned in different scenarios during competitive polo and horse racing. The data were used to evaluate the limits of turning performance. During high-speed turns of large radius horizontal speed was lower on the bend, as would be predicted from a model assuming a limb force limit to running speed. During small radius turns the angular velocity of heading decreased with increasing speed in a manner consistent with the coefficient of friction of the hoof-surface interaction setting the limit to centripetal force to avoid slipping.

Muscle contributions to propulsion and support during running

Muscles actuate running by developing forces that propel the body forward while supporting the body's weight. To understand how muscles contribute to propulsion (i.e., forward acceleration of the mass center) and support (i.e., upward acceleration of the mass center) during running we developed a three-dimensional muscle-actuated simulation of the running gait cycle. The simulation is driven by 92 musculotendon actuators of the lower extremities and torso and includes the dynamics of arm motion. We analyzed the simulation to determine how each muscle contributed to the acceleration of the body mass center. During the early part of the stance phase, the quadriceps muscle group was the largest contributor to braking (i.e., backward acceleration of the mass center) and support. During the second half of the stance phase, the soleus and gastrocnemius muscles were the greatest contributors to propulsion and support. The arms did not contribute substantially to either propulsion or support, generating less than 1% of the peak mass center acceleration. However, the arms effectively counterbalanced the vertical angular momentum of the lower extremities. Our analysis reveals that the quadriceps and plantarflexors are the major contributors to acceleration of the body mass center during running.

Biomechanical pole and leg characteristics during uphill diagonal roller skiing

Diagonal skiing as a major classical technique has hardly been investigated over the last two decades, although technique and racing velocities have developed substantially. The aims of the present study were to 1) analyse pole and leg kinetics and kinematics during submaximal uphill diagonal roller skiing and 2) identify biomechanical factors related to performance. Twelve elite skiers performed a time to exhaustion (performance) test on a treadmill. Joint kinematics and pole/plantar forces were recorded separately during diagonal roller skiing (9 degrees; 11 km/h). Performance was correlated to cycle length (r = 0.77; P < 0.05), relative leg swing (r = 0.71), and gliding time (r = 0.74), hip flexion range of motion (ROM) during swing (r = 0.73) and knee extension ROM during gliding (r = 0.71). Push-off demonstrated performance correlations for impulse of leg force (r = 0.84), relative duration (r= -0.76) and knee flexion (r = 0.73) and extension ROM (r = 0.74). Relative time to peak pole force was associated with performance (r = 0.73). In summary, diagonal roller skiing performance was linked to 1) longer cycle length, 2) greater impulse of force during a shorter push-off with larger flexion/extension ROMs in leg joints, 3) longer leg swing, and 4) later peak pole force, demonstrating the major key characteristics to be emphasised in training.

Functional specialization and ontogenetic scaling of limb anatomy in Alligator mississippiensis

Crocodylians exhibit a fascinating diversity of terrestrial gaits and limb motions that remain poorly described and are of great importance to understanding their natural history and evolution. Their musculoskeletal anatomy is pivotal to this diversity and yet only qualitative studies of muscle-tendon unit anatomy exist. The relative masses and internal architecture (fascicle lengths and physiological cross-sectional areas) of muscles of the pectoral and pelvic limbs of American alligators (Alligator mississippiensis Daudin 1801) were recorded for an ontogenetic series of wild specimens (n = 15, body masses from 0.5 to 60 kg). The data were analysed by reduced major axis regression to determine scaling relationships with body mass. Physiological cross-sectional areas and therefore muscle force-generating capacity were found to be greater in the extensor (anti-gravity) muscles of the pelvic limb than in the pectoral limb, reflecting how crocodylians differ from mammals in having greater loading of the hindlimbs than the forelimbs. Muscle masses and architecture were generally found to scale isometrically with body mass, suggesting an ontogenetic decrease in terrestrial athleticism. This concurs with the findings of previous studies showing ontogenetic decreases in limb bone length and the general scaling principle of a decline of strength : weight ratios with increasing size in animals. Exceptions to isometric scaling found included positive allometry in fascicle length for extensor musculature of both limbs, suggesting an ontogenetic increase in working range interpreted as increasing postural variability - in particular the major hip extensors - the interpretation of which is complicated by previous described ontogenetic increase of moment arms for these muscles.

The biological limits to running speed are imposed from the ground up

Running speed is limited by a mechanical interaction between the stance and swing phases of the stride. Here, we tested whether stance phase limitations are imposed by ground force maximums or foot-ground contact time minimums. We selected one-legged hopping and backward running as experimental contrasts to forward running and had seven athletic subjects complete progressive discontinuous treadmill tests to failure to determine their top speeds in each of the three gaits. Vertical ground reaction forces [in body weights (Wb)] and periods of ground force application (Tc; s) were measured using a custom, high-speed force treadmill. At top speed, we found that both the stance-averaged (Favg) and peak (Fpeak) vertical forces applied to the treadmill surface during one-legged hopping exceeded those applied during forward running by more than one-half of the body's weight (Favg = 2.71 ± 0.15 vs. 2.08 ± 0.07 Wb; Fpeak = 4.20 ± 0.24 vs. 3.62 ± 0.24 Wb; means ± SE) and that hopping periods of force application were significantly longer (Tc = 0.160 ± 0.006 vs. 0.108 ± 0.004 s). Next, we found that the periods of ground force application at top backward and forward running speeds were nearly identical, agreeing to within an average of 0.006 s (Tc = 0.116 ± 0.004 vs. 0.110 ± 0.005 s). We conclude that the stance phase limit to running speed is imposed not by the maximum forces that the limbs can apply to the ground but rather by the minimum time needed to apply the large, mass-specific forces necessary.

Two explanations for the compliant running paradox: reduced work of bouncing viscera and increased stability in uneven terrain

Economy is a central principle for understanding animal locomotion. Yet, compared with theoretical predictions concerning economy, animals run with compliant legs that are energetically costly. Here, we address this apparent paradox, highlighting two factors that predict benefits for compliant gaits: (i) minimizing cost of work associated with bouncing viscera; and (ii) leg control for robust stability in uneven terrain. We show that consideration of the effects of bouncing viscera predicts an energetic optimum for relatively compliant legs. To compare stability in uneven terrain, we introduce the normalized maximum drop (NMD), a measure based on simple kinematics, which predicts that compliant legs allow negotiation of relatively larger terrain perturbations without failure. Our model also suggests an inherent trade-off in control of leg retraction velocity (ω) for stability: low ω allows higher NMD, reducing fall risk, whereas high ω minimizes peak forces with terrain drops, reducing injury risk. Optimization for one of these factors explicitly limits the other; however, compliant legs relax this trade-off, allowing greater stability by both measures. Our models suggest compromises in leg control for economy and stability that might explain why animals run with compliant legs.

The use of MP3 recorders to log data from equine hoof mounted accelerometers

REASONS FOR PERFORMING STUDY

MP3 recorders are readily available, small, lightweight and low cost, providing the potential for logging analogue hoof mounted accelerometer signals for the characterisation of equine locomotion. These, however, require testing in practice.

OBJECTIVES

To test whether 1) multiple MP3 recorders can maintain synchronisation, giving the ability to synchronise independent recorders for the logging of multiple limbs simultaneously; and 2) features of a foot mounted accelerometer signal attributable to foot-on and foot-off can be accurately identified from horse foot mounted accelerometers logged directly into an MP3 recorder.

METHODS

Three experiments were performed: 1) Maintenance of synchronisation was assessed by counting the number of samples recorded by each of 4 MP3 recorders while mounted on a trotting horse and over 2 consecutive 30 min periods in 8 recorders on a bench. 2) Foot-on and foot-off times obtained from manual transcription of MP3 logged data and directly logged accelerometer signal were compared. 3) MP3/accelerometer acquisition units were used to log accelerometer signals from racehorses during extended training sessions.

RESULTS

Mean absolute error of synchronisation between MP3 recorders was 10 samples per million (compared to mean number of samples, range 1-32 samples per million). Error accumulation showed a linear correlation with time. Features attributable to foot on and foot off were equally identifiable from the MP3 recorded signal over a range of equine gaits.

CONCLUSIONS

Multiple MP3 recorders can be synchronised and used as a relatively cheap, robust, reliable and accurate logging system when combined with an accelerometer and external battery for the specific application of the measurement of stride timing variables across the range of equine gaits during field locomotion.

POTENTIAL RELEVANCE

Footfall timings can be used to identify intervals between the fore and hind contacts, the identification of diagonal advanced placement and to calculate stride timing variables (stance time, protraction time and stride time). These parameters are invaluable for the characterisation and assessment of equine locomotion.

Running-specific prostheses limit ground-force during sprinting

Running-specific prostheses (RSP) emulate the spring-like behaviour of biological limbs during human running, but little research has examined the mechanical means by which amputees achieve top speeds. To better understand the biomechanical effects of RSP during sprinting, we measured ground reaction forces (GRF) and stride kinematics of elite unilateral trans-tibial amputee sprinters across a range of speeds including top speed. Unilateral amputees are ideal subjects because each amputee's affected leg (AL) can be compared with their unaffected leg (UL). We found that stance average vertical GRF were approximately 9 per cent less for the AL compared with the UL across a range of speeds including top speed (p < 0.0001). In contrast, leg swing times were not significantly different between legs at any speed (p = 0.32). Additionally, AL and UL leg swing times were similar to those reported for non-amputee sprinters. We infer that RSP impair force generation and thus probably limit top speed. Some elite unilateral trans-tibial amputee sprinters appear to have learned or trained to compensate for AL force impairment by swinging both legs rapidly.

The effect of proprioceptive neuromuscular facilitation and static stretch training on running mechanics

Caplan, N, Rogers, R, Parr, MK, and Hayes, PR. The effect of proprioceptive neuromuscular facilitation and static stretch training on running mechanics. J Strength Cond Res 23(4): 1175-1180, 2009-There is a long-standing belief that increased range of movement (RoM) at the hip or knee will improve running mechanics; however, few studies have examined the effect of such an increase in RoM. The aim of this study was to determine the influence of 2 methods of stretch training (static and proprioceptive neuromuscular facilitation [PNF]) on high-velocity running. Eighteen rugby league players were assessed for maximum sprinting velocity. They were randomly allocated into 2 stretch training groups: PNF or static. Each group trained their hamstrings 4 d x w(-1) for 5 weeks. Pre- and posttraining subjects were videoed while running at 80% of maximum velocity. The video was digitized to identify biomechanical changes in hip flexion (HF), knee extension (KE), stride length (SL), stride rate (SR), and contact time (tc). Stretch training resulted in gains (p < 0.05) in HF for the static stretch (SS) (4.9%) and PNF (7.6%) groups. There were reductions in KE (p < 0.05) for SS (1.0%) and PNF (1.6%) groups. Stride mechanics were also altered after training. There were increases in SL (p < 0.05) for SS (7.1%) and PNF (9.1%) and a concomitant reduction in SR (p < 0.05) for SS (1.9%) and PNF (4.3%). No changes were observed in tc in either group. In conclusion, both SS and PNF training improved HF RoM and running mechanics during high-velocity running. These findings suggest that stretch training undertaken at the end of regular training is effective in changing running mechanics.

Mono- versus biarticular muscle function in relation to speed and gait changes: in vivo analysis of the goat triceps brachii

The roles of muscles that span a single joint (monoarticular) versus those that span two (biarticular) or more joints have been suggested to differ. Monoarticular muscles are argued to perform work at a joint, whereas biarticular muscles are argued to transfer energy while resisting moments across adjacent joints. To test these predictions, in vivo patterns of muscle activation, strain, and strain rate were compared using electromyography and sonomicrometry in two major elbow extensors, the long and lateral heads of the triceps brachii of goats (Capra hircus), across a range of speed (1-5 m s(-1)) and gait. Muscle recordings were synchronized to limb kinematics using high-speed digital video imaging (250 Hz). Measurements obtained from four goats (25-45 kg) showed that the monoarticular lateral head exhibited a stretch-shortening pattern (6.8+/-0.6% stretch and -10.6+/-2.7% shortening; mean+/-s.e.m. for all speeds and gaits) after being activated, which parallels the flexion-extension pattern of the elbow. By contrast, the biarticular long head shortened through most of stance (-16.4+/-3.4%), despite elbow flexion in the first half and shoulder extension in the last half of stance. The magnitude of elbow flexion and shoulder extension increased with increasing speed (ANCOVA, P<0.05 and P<0.001), as did the magnitude and rate of active stretch of fascicles in the lateral head (P<0.001 for both). In all individuals, shortening fascicle strain rates increased with speed in the long head (P<0.001), and, in three of the four individuals, strain magnitude increased. Few independent effects of gait were found. In contrast to its expected function, the biarticular long head appears to produce positive work throughout stance, whereas the monoarticular lateral head appears to absorb work at the elbow. The biarticular anatomy of the long head may mitigate increases in muscle strain with speed in this muscle, because strain magnitude in the second phase of stance (when the shoulder extends) decreased with speed (P<0.05).

The fastest runner on artificial legs: different limbs, similar function?

The recent competitive successes of a bilateral, transtibial amputee sprint runner who races with modern running prostheses has triggered an international controversy regarding the relative function provided by his artificial limbs. Here, we conducted three tests of functional similarity between this amputee sprinter and competitive male runners with intact limbs: the metabolic cost of running, sprinting endurance, and running mechanics. Metabolic and mechanical data, respectively, were acquired via indirect calorimetry and ground reaction force measurements during constant-speed, level treadmill running. First, we found that the mean gross metabolic cost of transport of our amputee sprint subject (174.9 ml O2·kg−1·km−1; speeds: 2.5–4.1 m/s) was only 3.8% lower than mean values for intact-limb elite distance runners and 6.7% lower than for subelite distance runners but 17% lower than for intact-limb 400-m specialists [210.6 (SD 13.2) ml O2·kg−1·km−1]. Second, the speeds that our amputee sprinter maintained for six all-out, constant-speed trials to failure (speeds: 6.6–10.8 m/s; durations: 2–90 s) were within 2.2 (SD 0.6)% of those predicted for intact-limb sprinters. Third, at sprinting speeds of 8.0, 9.0, and 10.0 m/s, our amputee subject had longer foot-ground contact times [+14.7 (SD 4.2)%], shorter aerial [−26.4 (SD 9.9)%] and swing times [−15.2 (SD 6.9)%], and lower stance-averaged vertical forces [−19.3 (SD 3.1)%] than intact-limb sprinters [top speeds = 10.8 vs. 10.8 (SD 0.6) m/s]. We conclude that running on modern, lower-limb sprinting prostheses appears to be physiologically similar but mechanically different from running with intact limbs.

Rapid acceleration in dogs: ground forces and body posture dynamics

Because the ability to accelerate rapidly is crucial to the survival and reproductive fitness of most terrestrial animals, it is important to understand how the biomechanics of rapid acceleration differs from that of steady-state locomotion. Here we compare rapid acceleration with high-speed galloping in dogs to investigate the ways in which body and limb posture and ground forces are altered to produce effective acceleration. Seven dogs were videotaped at 250 Hz as they performed `maximum effort' accelerations,starting in a standing position on a force plate and one and two strides before it. These dogs began accelerations by rapidly flexing their ankles and knees as they dropped into a crouch. The crouched posture was maintained in the first accelerating stride such that the ankle and knee were significantly more flexed than during steady high-speed galloping. The hindlimb was also significantly more retracted over the first stance period than during high-speed galloping. Ground forces differed from steady-state locomotion in that rapidly accelerating dogs supported only 43% of their body weight with the forelimbs, compared with 56–64% in steady-state locomotion. The hindlimbs applied greater peak accelerating forces than the forelimbs, but the forelimbs contributed significantly to the dogs' acceleration by producing 43%of the total propulsive impulse. Kinematically, rapid acceleration differs from steady-state galloping in that the limbs are more flexed and more retracted, while the back undergoes greater pitching movement. Ground reaction forces also differ significantly from steady-state galloping in that almost no decelerating forces are applied while propulsive force impulses are three to six times greater.

Undulation training for development of hierarchical fitness and improved firefighter job performance

Firefighters routinely encounter physical demands that contribute to countless musculoskeletal injuries. Seemingly, a progressive prescription for fitness would offer superior protection against intrinsic job risks. The purpose of this study was to investigate the influence of two resistance training interventions on fitness adaptations among firefighters, and to assess the degree of transfer to job-specific tasks. Firefighter trainees were recruited for participation in this experimental study. Two distinct, periodized training models-undulation training (UT; n = 7) and standard training control (STCo; n = 7)-were used to determine the differential affects for muscular fitness and transference to firefighter performance batteries. Specific tests were administered to evaluate 1) upper- and lower-body muscular strength, 2) lower-body power output, 3) sprint speed and jumping ability, 4) anthropometry, and 5) firefighter Grinder performance (i.e., firefighter-specific job tests). The 9-week UT experimental treatment prescription was characterized by daily "nonlinear" fluctuations in training to preferentially elicit specific and distinct muscular fitness components, whereas the STCo treatment conformed to a traditional model, in which each fitness component was systematically targeted during a specified mesocycle. For both treatments, nearly all fitness and performance measures significantly increased from baseline (p < 0.05), with a trend in favor of UT. Further, the UT group experienced significantly greater improvements (p < 0.05) in Grinder performance over the STCo group. Calculation of effect sizes identified meaningful differences in the magnitude of changes in outcomes (effect size > 0.50) in favor of UT for measures of thigh circumference, vertical jump, 1RM squat, Grinder performance, and peak power output. These findings suggest a potentially greater stimulus for multidimensional muscular fitness development with UT, over a periodized STCo. This study effectively establishes that UT may offer a greater transference to performance for firefighter-specific job tasks.

The evolutionary continuum of limb function from early theropods to birds

The bipedal stance and gait of theropod dinosaurs evolved gradually along the lineage leading to birds and at some point(s), flight evolved. How and when did these changes occur? We review the evidence from neontology and paleontology, including pectoral and pelvic limb functional morphology, fossil footprints/trackways and biomechanical models and simulations. We emphasise that many false dichotomies or categories have been applied to theropod form and function, and sometimes, these impede research progress. For example, dichotomisation of locomotor function into 'non-avian' and 'avian' modes is only a conceptual crutch; the evidence supports a continuous transition. Simplification of pelvic limb function into cursorial/non-cursorial morphologies or flexed/columnar poses has outlived its utility. For the pectoral limbs, even the classic predatory strike vs. flight wing-stroke distinction and separation of theropods into non-flying and flying--or terrestrial and arboreal--categories may be missing important subtleties. Distinguishing locomotor function between taxa, even with quantitative approaches, will always be fraught with ambiguity, making it difficult to find real differences if that ambiguity is properly acknowledged. There must be an 'interpretive asymptote' for reconstructing dinosaur limb function that available methods and evidence cannot overcome. We may be close to that limit, but how far can it be stretched with improved methods and evidence, if at all? The way forward is a combination of techniques that emphasises integration of neontological and paleontological evidence and quantitative assessment of limb function cautiously applied with validated techniques and sensitivity analysis of unknown variables.

Limits to running speed in dogs, horses and humans

Are there absolute limits to the speed at which animals can run? If so, how close are present-day individuals to these limits? I approach these questions by using three statistical models and data from competitive races to estimate maximum running speeds for greyhounds, thoroughbred horses and elite human athletes. In each case, an absolute speed limit is definable, and the current record approaches that predicted maximum. While all such extrapolations must be used cautiously, these data suggest that there are limits to the ability of either natural or artificial selection to produce ever faster dogs, horses and humans. Quantification of the limits to running speed may aid in formulating and testing models of locomotion.

Running-specific, periodized strength training attenuates loss of stride length during intense endurance running

The purpose of this study was to determine the effects of a running-specific, periodized strength training program (performed over the specific period [8 weeks] of a 16-week macrocycle) on endurance-trained runners' capacity to maintain stride length during running bouts at competitive speeds. Eighteen well-trained middle-distance runners completed the study (personal bests for 1500 and 5000 m of 3 minutes 57 seconds +/- 12 seconds and 15 minutes 24 seconds +/- 36 seconds). They were randomly assigned to each of the following groups (6 per group): periodized strength group, performing a periodized strength training program over the 8-week specific (intervention) period (2 sessions per week); nonperiodized strength group, performing the same strength training exercises as the periodized group over the specific period but with no week-to-week variations; and a control group, performing no strength training at all during the specific period. The percentage of loss in the stride length (cm)/speed (m.s) (SLS) ratio was measured by comparing the mean SLS during the first and third (last) group of the total repetitions, respectively, included in each of the interval training sessions performed at race speeds during the competition period that followed the specific period. Significant differences (p < 0.05) were found in mean percentage of SLS loss between the 3 study groups, with the periodized strength group showing no significant SLS change (0.36 +/- 0.95%) and the 2 other groups showing a moderate or high SLS loss (-1.22 +/- 1.5% and -3.05 +/- 1.2% for the nonperiodized strength and control groups, respectively). In conclusion, periodized, running-specific strength training minimizes the loss of stride length that typically occurs in endurance runners during fatiguing running bouts.

Effects of Velocity and Weight Support on Ground Reaction Forces and Metabolic Power during Running

The biomechanical and metabolic demands of human running are distinctly affected by velocity and body weight. As runners increase velocity, ground reaction forces (GRF) increase, which may increase the risk of an overuse injury, and more metabolic power is required to produce greater rates of muscular force generation. Running with weight support attenuates GRFs, but demands less metabolic power than normal weight running. We used a recently developed device (G-trainer) that uses positive air pressure around the lower body to support body weight during treadmill running. Our scientific goal was to quantify the separate and combined effects of running velocity and weight support on GRFs and metabolic power. After obtaining this basic data set, we identified velocity and weight support combinations that resulted in different peak GRFs, yet demanded the same metabolic power. Ideal combinations of velocity and weight could potentially reduce biomechanical risks by attenuating peak GRFs while maintaining aerobic and neuromuscular benefits. Indeed, we found many combinations that decreased peak vertical GRFs yet demanded the same metabolic power as running slower at normal weight. This approach of manipulating velocity and weight during running may prove effective as a training and/or rehabilitation strategy.

The acute effects of heavy back and front squats on speed during forty-meter sprint trials

The purpose of the present study was to investigate the effects of performing heavy back squats (HBS) and heavy front squats (HFS) on the average speed during each 10-m interval of 40-m sprint trials. In a randomized, cross-over design, 10 strength-trained men performed a HBS, HFS, or control treatment before performing three 40-m sprint trials separated by 3 minutes. The HBS and HFS treatments consisted of performing parallel back or front squats with 30%, 50%, and 70% of the subject's 1 repetition maximum after 5 minutes of cycling. The control treatment consisted of cycling for 5 minutes. The sprint trials were performed 4 minutes after completing the HBS, HFS, or control treatments. Significant increases in speed were found during the 10- to 20-m interval for the HBS compared with the control treatment (mean difference, 0.12 m x s(-1); 95% likely range, 0.05-0.18 m x s(-1); P = 0.001). During the 30- to 40-m interval, HBS produced significantly greater speeds compared with the HFS treatment (mean difference, 0.24 m x s(-1); 95% likely range, 0.02-0.45 m x s(-1); P = 0.034) and the control treatment (mean difference, 0.18 m x s(-1); 95% likely range, 0.03-0.32 m x s(-1); P = 0.021). The differing effects of the treatments may reflect different levels of muscular activation or different mechanical aspects of the squat exercises. Similarly, the multidimensional nature of sprint running means that other specific exercises may confer improvements in sprinting performance during other intervals. It is suggested that coaches could incorporate HBS into the warm-up procedure of athletes to improve sprinting performance.

Exercise-induced homeostatic perturbations provoked by singles tennis match play with reference to development of fatigue

This review addresses metabolic, neural, mechanical and thermal alterations during tennis match play with special focus on associations with fatigue. Several studies have provided a link between fatigue and the impairment of tennis skills proficiency. A tennis player's ability to maintain skilled on-court performance and/or optimal muscle function during a demanding match can be compromised as a result of several homeostatic perturbations, for example hypoglycaemia, muscle damage and hyperthermia. Accordingly, an important physiological requirement to succeed at competitive level might be the player's ability to resist fatigue. However, research evidence on this topic is limited and it is unclear to what extent players experience fatigue during high-level tennis match play and what the physiological mechanisms are that are likely to contribute to the deterioration in performance.

High-speed gallop locomotion in the thoroughbred racehorse. I. The effect of incline on stride parameters

During locomotion up an incline, power is required to elevate the centre of mass. This is provided when the animal's limbs are in contact with the ground. Measurements of stride timing variables from multiple limbs during high speed, over-ground locomotion would enhance our understanding of locomotor powering during changes in terrain. This study measured foot-on and foot-off times from galloping horses using a previously validated system of limb-mounted accelerometers and a global positioning system data logger. A detailed track survey provided incline information from all areas of the track. Measurements were made from six horses over a speed range of 9 to 13 m s(-1). Foot-fall timings were used to calculate variables, which included stance duration, protraction duration, stride frequency and duty factor. The relationship between track incline and measured variables was assessed. Stride variables from horses galloping on level (0-2% incline) and incline (8-12% incline) sections of the track were compared. Fore- and hindlimb protraction durations were significantly reduced across the speed range during incline galloping (P=0.001). This resulted in a mean increase in stride frequency from 2.01 to 2.08 strides s(-1) at 9.5 m s(-1) and 2.10 to 2.17 strides s(-1) at 12.5 m s(-1) during incline galloping. Duty factor was significantly greater for the hindlimbs during incline galloping (P<0.001), increasing from 0.31 to 0.32 at 9.5 m s(-1) and 0.28 to 0.29 at 12.5 m s(-1). Peak limb force was calculated from duty factor and assumed fore- to hindlimb impulse distributions. Smaller peak vertical forces were calculated in the forelimbs and increased peak vertical forces were calculated in the hindlimbs when galloping on an incline. Measured changes in stride timing variables differ from those reported in trotting horses. We propose that horses increase their stride frequency at a given speed during incline galloping to provide power for moving the centre of mass up the slope.

Runners do not push off the ground but fall forwards via a gravitational torque

The relationship between the affect and timing of the four forces involved in running (gravity, ground reaction force, muscle force, and potential strain energy) is presented. These forces only increase horizontal acceleration of the centre of mass during stance but not flight. The current hierarchical models of running are critiqued because they do not show gravity, a constant force, in affect during stance. A new gravitational model of running is developed, which shows gravity as the motive force. Gravity is shown to cause a torque as the runner's centre of mass moves forward of the support foot. Ground reaction force is not a motive force but operates according to Newton's third law; therefore, the ground can only propel a runner forward in combination with muscle activity. However, leg and hip extensor muscles have consistently proven to be silent during leg extension (mid-terminal stance). Instead, high muscle-tendon forces at terminal stance suggest elastic recoil regains most of the centre of mass's height. Therefore, the only external motive force from mid-terminal stance is gravity via a gravitational torque, which causes a horizontal displacement. The aim of this paper is to establish a definitive biomechanical technique (Pose method) that is easily taught to runners (Romanov, 2002): falling forwards via a gravitational torque while pulling the support foot rapidly from the ground using the hamstring muscles.

Track compliance does not affect sprinting performance

The aim of this study was to test the hypothesis that sprint performance (time over a given distance) would be affected by track compliance, with better performances on the more compliant surface. Ten sprinters participated in the study. The athletes performed maximal sprints (60 m) on three different track configurations (hard, 5500 kN m(-1); soft, 2200 kN m(-1); spring, 550 kN m(-1)). A 60-m single-lane running surface was constructed. Plywood boards (1.2 cm thick) were placed on a 60 x 0.6 m wooden chipboard frame serving as the base surface. All participants ran two times on each track configuration in a randomized order. The athletes' kinematics were recorded using the Vicon 624 system with 12 cameras operating at 250 Hz. Four Kistler force plates (1250 Hz) were used to record ground reaction forces. Sprint performance (time over 60 m) was unaffected by the different track compliances (P= 0.57). In addition, there was no effect of track (P> 0.05) on the sprinting kinematics and kinetics of the ankle or knee joint. The hypothesis that sprint performance is affected by track compliance can be rejected because the sprinters recorded similar performances while sprinting over 60 m on all three track configurations. We conclude that: (1) the possible deformation of the track while sprinting is minor enough not to cause a specific adjustment in the leg mechanics affecting the effectiveness of the stretch-shortening cycle of the sprinters; and (2) the energy exchange between sprinters and tracks has only a marginal effect on sprint performance due to its small magnitude. More research on tracks with lower stiffness is required.