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Acute Kinematic Effects of Sprinting With Motorized Assistance
Abstract
Clark, K, Cahill, M, Korfist, C, and Whitacre, T. Acute kinematic effects of sprinting with motorized assistance. J Strength Cond Res 35(7): 1856-1864, 2021-Although assisted sprinting has become popular for training maximum velocity, the acute effects are not fully understood. To examine this modality, 14 developmental male sprinters (age: 18.0 ± 2.5 years, 100-m personal best: 10.80 ± 0.31 seconds) performed maximal trials, both unassisted and assisted with a motorized towing device using a load of 7 kg (9.9 ± 0.9% body mass). Significant increases in maximum velocity (+9.4%, p ≤ 0.001, d = 3.28) occurred due to very large increases in stride length (+8.7%, p ≤ 0.001, d = 2.04) but not stride rate (+0.7%, p = 0.36, d = 0.11). Stride length increased due to small changes in distance traveled by the center of mass during ground contact (+3.7%, p ≤ 0.001, d = 0.40) combined with very large changes in distance traveled by the center of mass during flight (+13.1%, p ≤ 0.001, d = 2.62). Although stride rate did not demonstrate significant between-condition differences, the combination of contact and flight time was different. Compared to unassisted sprinting, assisted sprinting caused small but significant decreases in contact time (-5.2%, p ≤ 0.001, d = 0.49) and small but significant increases in flight time (+3.4%, p < 0.05, d = 0.58). Sprinting with motorized assistance elicited supramaximal velocities with decreased contact times, which may represent a neuromuscular stimulus for athletes attempting to enhance sprinting performance. Future research is needed to investigate the effects of this modality across various assistive loads and athletic populations, and to determine the longitudinal efficacy as a training method for improving maximum-velocity sprinting performance.
... Maximum running speed (MRS) is a specific and essential factor to stimulate specific performance in sprint disciplines in athletics [1,2]. Specific training for sprinters involves regular repetition of the motor pattern of the maximum speed running cycle [1]. ...
... Maximum running speed (MRS) is a specific and essential factor to stimulate specific performance in sprint disciplines in athletics [1,2]. Specific training for sprinters involves regular repetition of the motor pattern of the maximum speed running cycle [1]. Respecting the basic principle of biological stimuli specificity, two training methods for the improvement of MRS have been widely used: (1) those that use resisted speed stimuli, such as uphill running or with an overload on the athlete's running action through weighted vests or belts or with a towed sled [3], and (2) those that use assisted speed or overspeed (OS) through downhill running [4], high-speed treadmills [5] or towing systems (TS) [1,6,7], which provide assistance for the athlete to run at a speed greater than the maximum possible speed developed by themselves [1,8]. ...
... Specific training for sprinters involves regular repetition of the motor pattern of the maximum speed running cycle [1]. Respecting the basic principle of biological stimuli specificity, two training methods for the improvement of MRS have been widely used: (1) those that use resisted speed stimuli, such as uphill running or with an overload on the athlete's running action through weighted vests or belts or with a towed sled [3], and (2) those that use assisted speed or overspeed (OS) through downhill running [4], high-speed treadmills [5] or towing systems (TS) [1,6,7], which provide assistance for the athlete to run at a speed greater than the maximum possible speed developed by themselves [1,8]. OS stimuli increase the intensity in running movement specificity and physiologically stimulate the neuromuscular system during OS running actions [8,9]. ...
Overspeed is a training method used to improve running speed, although its effects are not supported by consensual scientific evidence. The overspeed stimulus can be boosted by several methods, including motorized towing devices. Our objectives were to analyze the acute effects of three overspeed loads in young athletes and to select optimal loads for training periods. Eight young athletes (16.73 ± 1.69 years) performed one unassisted sprint and three assisted sprints, and kinematic and biomechanical data were compared. Significant increases (p < 0.05) in step velocity and step length were found with 2, 4, and 5.25 kg in maximum running speed, flight time and horizontal distance from the first contact to the vertical projection of the center of mass with 4 and 5.25 kg. Significant time decreases were found in 5 m flying sprint and contact time with 4 and 5.25 kg, and no significant changes were observed in step rate. The individually recommended loads would be between 3.47 ± 0.68% and 6.94 ± 1.35% body weight. Even having limitations, we can understand this work and its results as a pilot study to replicate the methodology and the use of new devices to more broadly investigate the effects of overspeed.
... Two types (50 and 100 m) of supramaximal runs followed by a 20 m approach run with a smooth starting method [22,23]. The percentage increase in the velocity of a sprinter during supramaximal running is up to 110% [18,21,[24][25][26][27][28][29][30]. During our training, the rate was often set at 103-107% [17,21,[28][29][30][31]. Within this range, the sprinter could acquire a high stride frequency in a subjective sprinting motion. ...
... In Period III, in addition to the programs taken place in Period II, eccentric hamstring strengthening exercises (Nordic hamstring exercise [1,2], glute-ham raise exercises, [32] and dynamic stretching exercises) were added. The percentage increase in the velocity of a sprinter during supramaximal running is up to 110% [18,21,[24][25][26][27][28][29][30]. During our training, the rate was often set at 103-107% [17,21,[28][29][30][31]. Within this range, the sprinter could acquire a high stride frequency in a subjective sprinting motion. ...
Studies have not adequately addressed the influence of fatigue, which is considered a major risk factor for hamstring injuries. Therefore, this study aimed to clarify how a muscle fatigue condition affects the success of hamstring injury prevention programs in sprinters. The study subjects were 613 collegiate male sprinters. They employed submaximal/maximal running for a large number of runs and supramaximal running for a small number of runs in daily training. The hamstring injury prevention program had become the most effective strategy in the past 24 seasons of track and field for preventing hamstring injuries. The number of sprinters who experienced hamstring injuries in three periods over the 24 seasons was recorded. The incidents of hamstring injuries during supramaximal running per athlete-seasons were 137.9, 60.6, and 6.7 for Periods I, II, and III, respectively, showing a significant decline (p < 0.01). Furthermore, the incidents of hamstring injuries during submaximal and maximal running per season showed no significant change. The results of this study indicate that by inducing muscle fatigue, a small number of runs makes hamstring injury prevention programs effective.
... The first reason is that, as Hicks [7] reports, in most studies stride length increases, and stride frequency decreases or remains steady in supramaximal running. Even in research using a towing device that may offer precise control of assistance compared with other modes of overspeed training, a significant increase was observed in stride length but not stride frequency [8]. This may suggest that supramaximal running may not provide a transfer any greater than that provided by standard maximal running [9]. ...
... In our training, towing was performed using a towing machine [5,6,8,17] and a rubber tube [1,7] (Figure 2). The towing machine used allowed sprinters to be towed for ≥100 m. ...
(1) Background: Although innovations and improvements in towing systems have been available, tow-training method has not been considered favored in the training context. Tow-training may enable high stride frequency if hamstring injuries do not occur. The purpose of this study was to prevent hamstring injuries during supramaximal running and to optimize tow-training. (2) Methods: We investigated the relationship between the number of hamstring injuries that occurred during supramaximal running and the contents of the prevention programs that have been implemented, i.e., 4 years of the baseline programs and 12 years of the intervention. (3) Results: The incidence of hamstring injuries per 1000 sprinters was 57.5 for baseline and 6.7 for intervention. A significant difference was observed in the incidence of hamstring injury between the different combinations of prevention programs (p < 0.01). (4) Conclusions: Tow-training was optimized by (1) preventing hamstring injuries by combination of strength, agility, and flexibility training programs and (2) advising the sprinters to press the leg onto the ground as fast as possible to increase stride frequency and to prevent stride lengthening.
... Considering the recent research interest in the 1080 Sprint as a training tool [17][18][19][20][21][22] and measurement device 3 and given its increasing use by coaches and sport scientists, it seems prudent to establish the agreement between data calculated from the 1080 Sprint and an alternative technology already widely used in practice, a radar device. More specifically, it is of interest to understand if measures collected with one device can be compared to measures collected by the other device in situations where athletes may train in facilities which have different devices or in a facility which has both devices. ...
This study established the magnitude of systematic bias and random error of horizontal force-velocity (F-v) profile variables obtained from a 1080 Sprint compared to that obtained from a Stalker ATS II radar device. Twenty high-school athletes from an American football training group completed a 30 m sprint while the two devices simultaneously measured velocity-time data. The velocity-time data were modelled by an exponential equation fitting process and then used to calculate individual F-v profiles and related variables (theoretical maximum velocity, theoretical maximum horizontal force, slope of the linear F-v profile, peak power, time constant tau, and horizontal maximal velocity). The devices were compared by determining the systematic bias and the 95% limits of agreement (random error) for all variables, both of which were expressed as percentages of the mean radar value. All bias values were within 6.32%, with the 1080 Sprint reporting higher values for tau, horizontal maximal velocity, and theoretical maximum velocity. Random error was lowest for velocity-based variables but exceeded 7% for all others, with slope of the F-v profile being greatest at ±12.3%. These results provide practitioners with the information necessary to determine if the agreement between the devices and the magnitude of random error is acceptable within the context of their specific application.
... Nonspecific methods of improving sprint performance primarily include resistance training, plyometric training, or a combination of both, with varied responses observed across different stages of maturation (16). Specific training includes modes of training that more closely reflect the demands and movement patterns of sprinting, such as free, assisted, and resisted sprinting (4,6,26). Supporting the concept of training specificity, sprint-specific methods of training have been shown to improve sprint performance in young athletes to a greater extent than nonsprint specific methods (30). ...
Cahill, MJ, Oliver, JL, Cronin, JB, Clark, K, Cross, MR, Lloyd, RS, and Lee, JE. Influence of resisted sled-pull training on the sprint force-velocity profile of male high-school athletes. J Strength Cond Res XX(X): 000-000, 2020-Although resisted sled towing is a commonly used method of sprint-specific training, little uniformity exists around training guidelines for practitioners. The aim of this study was to assess the effectiveness of unresisted and resisted sled-pull training across multiple loads. Fifty-three male high-school athletes were assigned to an unresisted (n 5 12) or 1 of 3 resisted groups: light (n 5 15), moderate (n 5 14), and heavy (n 5 12) corresponding to loads of 44 6 4 %BM, 89 6 8 %BM, and 133 6 12 %BM that caused a 25, 50, and 75% velocity decrement in maximum sprint speed, respectively. All subjects performed 2 sled-pull training sessions twice weekly for 8 weeks. Split times of 5, 10, and 20 m improved across all resisted groups (d 5 0.40-1.04, p , 0.01) but did not improve with unresisted sprinting. However, the magnitude of the gains increased most within the heavy group, with the greatest improvement observed over the first 10 m (d $ 1.04). Changes in preintervention to postintervention force-velocity profiles were specific to the loading prescribed during training. Specifically, F 0 increased most in moderate to heavy groups (d 5 1.08-1.19); Vmax significantly decreased in the heavy group but increased in the unresisted group (d 5 012-0.44); whereas, Pmax increased across all resisted groups (d 5 0.39-1.03). The results of this study suggest that the greatest gains in short distance sprint performance, especially initial acceleration, are achieved using much heavier sled loads than previously studied in young athletes.
... Non-specific methods of improving sprint performance primarily include resistance training, plyometric training or a combination of both, with varied responses observed across different stages of maturation 121 . Specific training includes modes of training that more closely reflect the demands and movement patterns of sprinting, such as free, assisted and resisted sprinting 50,122 . Supporting the concept of training specificity, sprint-specific methods of training have been shown to improve sprint performance in young athletes to a greater extent than non-sprint specific methods 55 . ...
Speed is an important athletic quality and needs to be developed in young athletes, this may be best achieved using specific forms of sprint training. Resisted sled training is a sprint specific form of training widely used by coaches and practitioners. The two modes of resisted sled training that exist are sled pushing and pulling, with limited research available for pulling and little, if any, available for pushing in any population. The overarching question that guided this thesis was “what are the acute and chronic training responses to sled pushing and pulling in young athletes?”
The aims of the thesis were to: review existing literature related to acute and chronic training responses to resisted sled pushing and pulling; examine the reliability, linearity, and utility of individual load-velocity profiles to prescribe training loads during sled pushing and pulling in young athletes; assess the effectiveness of unresisted and resisted sled pull and sled push training on short distance sprint performance across a wide array of individualised loads; and, provide practical programming guidelines on how to integrate resisted sled training into an athlete’s training.
The main findings of this thesis were: 1) across existing literature little uniformity exists with regard to prescription of load for resisted sled training although heavier loads appeared to provide a stimulus for higher horizontal force application. Loads can be applied across different zones of training such as technical competency, speed-strength, power and strength-speed. 2) Sled pushing and pulling produce a highly linear relationship (r > 0.95) between load and velocity. The slope of the load-velocity relationship was found to be reliable (CV = 3.1%), with the loads that cause a decrement in velocity of 25, 50 and 75% also found to be reliable (CVs = <5%). However, there was large between-participant variation (95%CI) in the load that caused a given Vdec in both sled pushing and pulling. Loads of 14-21, 36-53, 71-107 and 107-160% body mass (%BM) caused a Vdec of 10, 25, 50 and 75% in sled pulling. Loads of 23-42, 45-85 and 69-131% body mass (%BM) caused a Vdec of 25, 50 and 75% in sled pushing. 3) Both forms of resisted sprint training demonstrated a clear trend for greater and more consistent improvements in sprinting force, power and performance over short distances when training with heavier sled loads (as compared to a lighter load or unresisted sprint training).
Several practical applications may be offered from the findings. Due to the linearity and reliability of the load-velocity relationship, coaches are urged to prescribe individualised sled loads based on a target decrement in velocity rather than simply prescribing all athletes the same load as a set percentage of body mass. Both sled pushing and pulling were effective sprint specific modes of training to enhance overall sprint performance, with the latter found to be more sprint specific due to the use of the arms. Heavier loads during both forms of resisted sled training appeared to yield the greatest benefit to young athletes in short distance sprint performance, however a targeted approach to sled loading may influence different phases of the sprint.
Speed is a crucial element an athlete must possess to be successful. In soccer, the
ability to accelerate faster than your opponent can result in being first to reach a ball on
a breakaway or stopping a counter attack. A unique way to train explosive movements
is to evoke postactivation potentiation (PAP) in the working muscles. Traditionally, an
overload stimulus with a long rest period is used, but a model utilizing an overspeed
stimulus with shorter rest periods is less understood. Therefore, the purpose of this
study was to determine the acute effects of varied rest intervals following assisted
sprinting on bodyweight sprint time. Twenty-four female soccer players were split into
two groups: recreational (n:11; age:20±1.67yrs; ht:162.30±4.35cm;
mass:61.02±8.78kg) and collegiate athletes (n:13; age:19.76±0.83yrs;
ht:166.85±5.98cm; mass:61.23±3.77kg). All participants attended five separate
sessions, performed a dynamic warm up, then executed one 20m sprint (with 5m
splits) at 30% bodyweight assistance (BWA). They then rested for 30s, one, two, or
4min in random order, followed by one bodyweight sprint with no BWA. Baseline sprint
times were measured without BWA on the initial session of testing. Results revealed no
difference in sprint time for the full 20m distance in either group. However, sprint time
was significantly decreased for the 0-5m split only for the athletes following 1min
(1.15±0.06s) and 2min (1.16±0.06s) rest compared to baseline (1.21±0.04s).
Therefore, trained athletes should rest one or two minutes after 30% BWA
supramaximal sprinting for increased bodyweight sprint speed.
This study aimed to compare the force (F)-velocity (v)-power (P)-time (t) relationships of female and male world-class sprinters. A total of 100 distance-time curves (50 women and 50 men) were computed from international 100-m finals, to determine the acceleration and deceleration phases of each race: (a) mechanical variables describing the velocity, force, and power output; and (b) F-P-v relationships and associated maximal power output, theoretical force and velocity produced by each athlete (Pmax , F0 , and V0 ). The results showed that the maximal sprint velocity (Vmax ) and mean power output (W/kg) developed over the entire 100 m strongly influenced 100-m performance (r > -0.80; P ≤ 0.001). With the exception of mean force (N/kg) developed during the acceleration phase or during the entire 100 m, all of the mechanicals variables observed over the race were greater in men. Shorter acceleration and longer deceleration in women may explain both their lower Vmax and their greater decrease in velocity, and in turn their lower performance level, which can be explained by their higher V0 and its correlation with performance. This highlights the importance of the capability to keep applying horizontal force to the ground at high velocities.
Overspeed exercises are commonly integrated into a training program to help athletes perform at a speed greater than what they are accustomed to when unassisted. However, the optimal assistance for maximal sprinting has not been determined. The purpose of this study was to determine the optimal elastic cord assistance for sprinting performance. Eighteen collegiate women soccer players completed 3 testing sessions, which consisted of a 5-minute warm-up, followed by 5 randomized experimental conditions of 0, 10, 20, 30, and 40% body weight assistance (BWA). In all BWA sessions, subjects wore a belt while attached to 2 elastic cords and performed 2 maximal sprints under each condition. Five minutes of rest was given between each sprint attempt and between conditions. Split times (0-5, 5-10, 10-15, 15-20, and 0-20 yd) for each condition were used for analysis. Results for 0-20 yd demonstrated a significant main effect for condition. Post hoc comparisons revealed that as BWA increased, sprint times decreased up to 30% BWA (0%: 3.20 ± 0.12 seconds; 10%: 3.07 ± 0.09 seconds; 20%: 2.96 ± 0.07 seconds; 30%: 2.81 ± 0.08 seconds; 40%: 2.77 ± 0.10 seconds); there was no difference between 30 and 40% BWA. There was also a main effect for condition when examining split times. Post hoc comparisons revealed that as BWA increased, sprint times decreased up to 30% BWA for distances up to 15 yd. These results demonstrate that 30% of BWA with elastic cords appears optimal in decreasing sprint times in collegiate women soccer players for distances up to 15 yd.
The purpose of this study was to determine the influence of towing force magnitude on the kinematics of supramaximal sprinting. Ten high school and college-age track and field athletes (6 men, 4 women) ran 60-m maximal sprints under 5 different conditions: Nontowed, Tow A (2.0% body weight [BW]), Tow B (2.8% BW), Tow C (3.8% BW), and Tow D (4.7% BW). Three-dimensional kinematics of a 4-segment model of the right side of the body were collected starting at the 35-m point of the trial using high-speed (250 Hz) optical cameras. Significant differences (p < 0.05) were observed in stride length and horizontal velocity of the center of mass during Tow C and Tow D. For Tow D, a significant increase (p = 0.046) in the distance from the center of mass to the foot at touchdown was also observed. Contact time decreased significantly in all towing conditions (p < 0.01), whereas stride rate increased only slightly (<2.0%) under towed conditions. There were no significant changes in joint or segment angles at touchdown, with the exception of a significant decrease (p = 0.044) in the flexion/extension angle at the hip during the Tow D condition. We conclude that towing force magnitude does influence the kinematics of supramaximal running and that potentially negative training effects may arise from towing individuals with a force in excess of 3.8% BW. Therefore, we suggest that coaches and practitioners adjust towing force magnitude for each individual and avoid using towing forces in excess of 3.8% of the athlete's BW.
There is substantial evidence that static stretching may inhibit performance in strength and power activities. However, most of this research has involved stretching routines dissimilar to those practiced by athletes. The purpose of this study was to evaluate whether the decline in performance normally associated with static stretching pervades when the static stretching is conducted prior to a sport specific warm-up. Thirteen netball players completed two experimental warm-up conditions. Day 1 warm-up involved a submaximal run followed by 15 min of static stretching and a netball specific skill warm-up. Day 2 followed the same design; however, the static stretching was replaced with a 15 min dynamic warm-up routine to allow for a direct comparison between the static stretching and dynamic warm-up effects. Participants performed a countermovement vertical jump and 20m sprint after the first warm-up intervention (static or dynamic) and also after the netball specific skill warm-up. The static stretching condition resulted in significantly worse performance than the dynamic warm-up in vertical jump height (-4.2%, 0.40 ES) and 20m sprint time (1.4%, 0.34 ES) (p<0.05). However, no significant differences in either performance variable were evident when the skill-based warm-up was preceded by static stretching or a dynamic warm-up routine. This suggests that the practice of a subsequent high-intensity skill based warm-up restored the differences between the two warm-up interventions. Hence, if static stretching is to be included in the warm-up period, it is recommended that a period of high-intensity sport-specific skills based activity is included prior to the on-court/field performance.
High-speed actions are known to impact soccer performance and can be categorized into actions requiring maximal speed, acceleration, or agility. Contradictory findings have been reported as to the extent of the relationship between the different speed components. This study comprised 106 professional soccer players who were assessed for 10-m sprint (acceleration), flying 20-m sprint (maximum speed), and zigzag agility performance. Although performances in the three tests were all significantly correlated (p < 0.0005), coefficients of determination (r(2)) between the tests were just 39, 12, and 21% for acceleration and maximum speed, acceleration and agility, and maximum speed and agility, respectively. Based on the low coefficients of determination, it was concluded that acceleration, maximum speed, and agility are specific qualities and relatively unrelated to one another. The findings suggest that specific testing and training procedures for each speed component should be utilized when working with elite players.
A comparison of resistance running, normal sprint running, and supramaximal running was performed. Nineteen young, generally well-trained subjects were divided into 3 training groups: resistance, normal, and supramaximal groups. Resistance and supramaximal training was done using a towing device, providing extra resistance or propulsion forces, resulting in running speed differences of about 3.3% (supramaximal) and 8.5% (resistance), compared to normal sprinting. The training period was 6 weeks, with 3 training sessions per week (5 sprint-runs over 22 m). Running times were measured using photocells, and average step length and cadence were recorded by digital video. A small (0.5%) but significant (p < 0.05) overall pre-post difference was found in running velocity, but the 3 groups changed differently over the running conditions. All individual subjects improved sprinting velocity most on the trained form, at 1-2% (p < 0.001), and thus, the principle of velocity specificity in sprint training was supported. This indicates that to obtain short-distance sprinting improvement in a short period of time, one may prefer normal sprinting over other training forms.
The relationship between gait mechanics and running ground reaction forces is widely regarded as complex. This viewpoint has evolved primarily via efforts to explain the rising-edge of vertical force-time waveforms observed during slow human running. Existing theoretical models do provide good rising-edge fits, but require more than a dozen input variables to sum the force contributions of four or more vague components of the body's total mass (mb). Here, we hypothesized that the force contributions of two discrete body mass components are sufficient to account for vertical ground reaction force-time waveforms patterns in full [stance foot and shank, m1=0.08•mb; remaining mass, m2=0.92•mb]. We tested this hypothesis directly by acquiring simultaneous limb motion and ground reaction force data across a broad range of running speeds (3.0-11.1 m•s(-1)) from 42 subjects who differed in body mass (range: 43-105 kg) and foot-strike mechanics. Predicted waveforms were generated from our two-mass model using body mass and three stride-specific measures: contact time, aerial time, and lower-limb vertical acceleration during impact. Measured waveforms (n=500) differed in shape and varied by more than two-fold in amplitude and duration. Nonetheless, the overall agreement between the 500 measured waveforms and those generated independently by the model approached unity (R(2)=0.95±0.04; mean±sd), with minimal variation across the slow, medium and fast running speeds tested (ΔR(2)≤0.04), and between rear-foot (R(2)=0.94±0.04, n=177) vs. fore-foot (R(2)=0.95±0.04, n=323) strike mechanics. We conclude that two, anatomically-discrete components of the body's mass are sufficient to fully explain running vertical ground reaction forces.
The effects of running at supramaximal velocity on biomechanical variables were studied in 13 male and 9 female sprinters. Cinematographical analysis was employed to investigate the biomechanics of the running technique. In supramaximal running the velocity increased by 8.5%, stride rate by 1.7%, and stride length by 6.8% over that of the normal maximal running. The elite male sprinters increased their stride rate significantly but did not increase their stride length. The major biomechanical differences between supramaximal and maximal running occurred during the contact phase. In supramaximal running the inclination of the ground shank at the beginning of eccentric phase was more "braking" and the angle of the ground knee was greater. During the ground contact phase, the maximal horizontal velocity of the swinging thigh was faster. The duration of the contact phase was shorter and the flight phase was longer in the supramaximal run as compared to the maximal run. It was concluded that in supramaximal effort it is possible to run at a higher stride rate than in maximal running. Data suggest that supramaximal sprinting can be beneficial in preparing for competition and as an additional stimulus for the neuromuscular system during training. This may result in adaptation of the neuromuscular system to a higher performance level.
The gaits of reptiles, birds, and mammals are reviewed. It is shown that mammals of different sizes tend to move in dynamically similar fashion whenever their Froude numbers u**2/gh are equal: here u is speed, g is the acceleration of free fall, and h is the height of the hip joint from the ground. The gaits of turtles and people are examined in detail. The gaits of turtles appear to reduce unwanted displacements (pitch, roll, etc. ) to the minimum possible for animals with such slow muscles. The patterns of force exerted in human walking and running minimize the work required of the muscles at each speed. This work is pertinent to robotics.
Data of elite sprinters indicate that faster athletes realize shorter ground contact times compared to slower individuals. Further, the importance of the so called ´front side mechanics´ for elite sprint performance is frequently emphasized by researchers and coaches. Recently it was demonstrated that using a body-weight supporting kite during full effort sprints in highly trained sprinters leads to a reduction in ground contact time. The aim of this study was to investigate possible negative effects of this body-weight supporting device on sprint running kinematics, which was not clarified in previous studies. Eleven well trained Austrian sprinters performed flying 20m-sprints under two conditions: (1) free sprint (FS); and (2) body-weight supported sprint (BWS). Sprint cycle characteristics were recorded during the high-speed phase by a 16 camera 3D-system (Vicon), an optical acquisition system (Optojump-next), and a high-speed camera. Paired sample t-tests and Cohen's d effect-size were used to determine differences between sprinting conditions. Compared to FS, BWS caused a decrease in ground contact time by 5.6% and an increase in air time by 5.5% (both p<0.001), whereas stride length and rate remained unchanged. Furthermore, a reduced hip joint extension at and after take-off, an increased maximal hip joint flexion (i.e. high knee position), and a smaller horizontal distance of the touchdown to the centre of gravity could be observed (all p<0.01). These results indicate no negative effects on ´front side mechanics´ during BWS and that sprinting with a body-weight supporting kite appears to be a highly specific method to reduce ground contact time in well trained sprinters.
Are the fastest running speeds achieved using the simple-spring stance mechanics predicted by the classic spring-mass model? We hypothesized that a passive, linear-spring model would not account for the running mechanics that maximize ground force application and speed. We tested this hypothesis by comparing patterns of ground force application across athletic specialization (competitive sprinters vs. athlete non-sprinters; n=7 each) and running speed (top speeds vs. slower ones). Vertical ground reaction forces at 5.0 m•s(-1), 7.0 m•s(-1) and individual top speeds (n=797 total footfalls) were acquired while subjects ran on a custom, high-speed force treadmill. The goodness of fit between measured vertical force vs. time waveform patterns and the patterns predicted by the spring-mass model were assessed using the R(2) statistic (where an R(2) of 1.00 = perfect fit). As hypothesized, the force application patterns of the competitive sprinters deviated significantly more from the simple-spring pattern than those of the athlete, non-sprinters across the three test speeds (R(2) < 0.85 vs. R(2) ≥ 0.91, respectively), and deviated most at top speed (R(2)=0.78±0.02). Sprinters attained faster top speeds than non-sprinters (10.4±0.3 vs. 8.7±0.3 m•s(-1)) by applying greater vertical forces during the first half (2.65±0.05 vs. 2.21±0.05 body weights), but not the second half (1.71±0.04 vs. 1.73±0.04 body weights) of the stance phase. We conclude that a passive, simple-spring model has limited application to sprint running performance because the swiftest runners use an asymmetrical pattern of force application to maximize ground reaction forces and attain faster speeds.
Running performance, energy requirements, and musculoskeletal stresses are directly related to the action-reaction forces between the limb and ground. For human runners, the force-time patterns from individual footfalls can vary considerably across speed, foot-strike, and footwear conditions. Here, we used four human footfalls with distinctly different vertical force-time waveform patterns to evaluate whether a basic mechanical model might explain all of them. Our model partitions the body's total mass (1.0 Mb) into two invariant mass fractions (lower-limb=0.08, remaining body mass=0.92) and allows the instantaneous collisional velocities of the former to vary. The best fits achieved (R(2) range: 0.95-0.98, mean=0.97±0.01) indicate that the model is capable of accounting for nearly all of the variability observed in the four waveform types tested: barefoot jog, rear-foot strike run, fore-foot strike run, and fore-foot strike sprint. We conclude that different running ground reaction force-time patterns may have the same mechanical basis.
The gaits of reptiles, birds, and mammals are reviewed. It is shown that mammals of different sizes tend to move in dy namically similar fashion whenever their Froude numbers u2/gh are equal: here u is speed, g is the acceleration of free fall, and h is the height of the hip joint from the ground. The gaits of turtles and people are examined in detail. The gaits of turtles appear to reduce unwanted displacements (pitch, roll, etc.) to the minimum possible for animals with such slow muscles. The patterns of force exerted in human walking and running minimize the work required of the muscles at each speed. Much of the energy that would otherwise be neededfor running, by people and other large mammals, is saved by tendon elasticity.
HIGH-SPEED TREADMILLS HAVE BECOME VALUABLE TOOLS FOR INCREASING SPEED AND SPORTS PERFORMANCE OVER THE PAST 2 DECADES. TRADITIONALLY, THEY HAVE BEEN PART OF NARROWLY FOCUSED CLINIC-BASED PROGRAMS DESIGNED TO INCREASE SPEED SOLELY WITH THE USE OF TECHNOLOGY. THIS HAS LED TO QUESTIONS ABOUT SURFACE TRANSFER, HIGH INJURY RATES, AND HOW THIS TECHNOLOGY FITS INTO A COMPREHENSIVE STRENGTH AND CONDITIONING PROGRAM. HERE, WE WILL NOT ONLY ADDRESS THESE ISSUES BUT ALSO DEMONSTRATE THAT WHEN PROPERLY INTEGRATED, HIGH-SPEED TREADMILLS ARE EXCEPTIONAL TOOLS THAT CAN BE USED IN A VARIETY OF SETTINGS TO IMPROVE PERFORMANCE FOR THE SPEED AND POWER ATHLETES WHILE ALL BUT ELIMINATING SPRINT-RELATED INJURIES.
It is well founded that ground contact time is the crucial part of sprinting because the available time window to apply force to the ground diminishes with growing running velocity. In view of this knowledge, the purpose of this study was to investigate the effects of body-weight support during full-effort sprints on ground contact time and selected stride parameters in 19 Austrian male elite sprinters. A kite with a lifting effect combined with a towing system to erase drag was utilized. Subjects performed flying 20m-sprints under three conditions: (i) free sprint; (ii) body-weight supported sprint - normal speed (BWS-NS); and (iii) body-weight supported sprint - overspeed (BWS-OS). Sprint cycle characteristics were recorded during the high-speed phase by an optical acquisition system. Additionally, running velocity was calculated from the 20m-sprint time. Compared to the fastest free sprint, running velocity, step length, and step frequency remained unchanged during BWS-NS, while ground contact time decreased (-5.80%), and air time increased (+5.79%) (both p<0.001). Throughout, BWS-OS ground contact time (-7.66%) was reduced, whereas running velocity (+2.72%), air time (+4.92%), step length (+1.98%) (all p<0.001), and step frequency (+1.05%; p<0.01) increased. Compared to BWS-NS, BWS-OS caused an increase in running velocity (+3.33%), step length (+1.92%) (both p<0.001), and step frequency (+1.37%; p<0.01), while ground contact time was diminished (-1.97%; p<0.001). In summary, sprinting with a body-weight supporting kite appeared to be a highly specific method to simulate an advanced performance level, indicated by higher running velocities requiring reduced ground contact times. The additional application of an overspeed condition led to a further reduction of ground contact time. Therefore, we recommend body-weight supported sprinting as an additional tool in sprint training.
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.
The proper selection of equipment is vital to the ability to accurately measure and track changes in performance. When measuring sprint time, electronic timing systems are recommended but may contain significant errors when an arm or leg passes through a gate before the torso. Dual-photocell (DP) and signal processing systems have been developed to overcome these issues. Ten subjects performed 10× 10-m sprints during which split time was calculated using 3 timing systems: a single photocell (SP) and DP without processing and a no-reflector gate with signal processing. The DP had fewer false signals compared with the SP (7, 14); however, signal processing eliminated all false signals. The mean differences between the 3 timing systems ranged from 9 to 17 milliseconds; however, the SD ranged 12-42 milliseconds because of the occurrence of false signals. When performing repeated 10-m sprints, it is vital to have a system that reduces or eliminates the occurrence of false signals, or training adaptations are likely to be overlooked. Thus, for 10-m sprints or splits, a timing system that reduces the incidence of false signals is needed (either DP or gates signal processing), and the use of an SP system without internal processing is inappropriate. However, as the distance and the expected adaptations increase, a smaller proportion of the adaptation is likely to be confounded when using an SP system.
This investigation evaluated the effects of a 4-week, 12-session training program using resisted sprint training (RST), assisted sprint training (AST), and traditional sprint training (TST) on maximal velocity and acceleration in National Collegiate Athletic Association (NCAA) Division IA female soccer athletes (n = 27). The subjects, using their respective training modality, completed 10 maximal effort sprints of 20 yd (18.3 m) followed by a 20-yd (18.3 m) deceleration to jog. Repeated measures multivariate analyses of variance and analyses of variance demonstrated significant (p < 0.001) 3-way interactions (time × distance × group) and 2-way interactions (time × group), respectively, for both velocity and acceleration. Paired t-tests demonstrated that maximum 40-yd (36.6-m) velocity increased significantly in both the AST (p < 0.001) and RST (p < 0.05) groups, with no change in the TST group. Five-yard (4.6-m), 15-yd (13.7 m), 5- to 15-yd (4.6- to 13.7-m) acceleration increased significantly (p < 0.01) in the AST group and did not change in the RST and TST groups. Fifteen- to 25-yd (13.7- to 22.9-m) acceleration increased significantly (p < 0.01) in the RST group, decreased significantly (p < 0.01) in the AST group, and was unchanged in the TST group. Twenty-five to 40-yd (22.9- to 36.6-m) acceleration increased significantly (p < 0.05) in the RST group and remained unchanged in the AST and TST groups. It is purposed that the increased 5-yd (4.6-m) and 15-yd (13.7-m) accelerations were the result of enhanced neuromuscular facilitation in response to the 12-session supramaximal training protocol. Accordingly, it is suggested that athletes participating in short distance acceleration events (i.e., ≤15 yd; ≤13.7 m) use AST protocols, whereas athletes participating in events that require greater maximum velocity (i.e., >15 yd; > 13.7 m) should use resisted sprint training protocols.
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 (W(b))] and periods of ground force application (T(c); s) were measured using a custom, high-speed force treadmill. At top speed, we found that both the stance-averaged (F(avg)) and peak (F(peak)) 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 (F(avg) = 2.71 +/- 0.15 vs. 2.08 +/- 0.07 W(b); F(peak) = 4.20 +/- 0.24 vs. 3.62 +/- 0.24 W(b); means +/- SE) and that hopping periods of force application were significantly longer (T(c) = 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 (T(c) = 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.
This study evaluated a variety of downhill slopes in an effort to determine the optimal slope for overspeed running.
Thirteen NCAA Division III college athletes who participated in soccer, track, and football ran 40-yd (36.6-m) sprints, on downhill slopes of 2.1 degrees , 3.3 degrees , 4.7 degrees , 5.8 degrees , and 6.9 degrees in random order. All sprints were timed using the Brower Timing System Speedtrap II. Data were analyzed with SSPS 15.0. A 1-way repeated-measures analysis of variance revealed significant main effects for the test slopes (P = .000). Bonferroni-adjusted pairwise comparisons determined that there were a number of differences between the hill slopes.
Analysis reveals that 40-yd sprints performed on hill slopes of approximately 5.8 degrees were optimal compared with flatland running and the other slopes assessed (P < .05). Sprinting on a 5.8 degrees slope increased the subjects' maximal speed by an average of 0.35 s, resulting in a 6.5% +/- 4.0% decrease in 40-yd sprint time compared with flatland running. Compared with the 4.7 degrees slope, the 5.8 degrees slope yielded a 0.10-s faster 40-yd sprint time, resulting in a 1.9% increase in speed.
Those who train athletes for speed should use or develop overspeed hills with slopes of approximately 5.8 degrees to maximize acute sprinting speed. The results of this study bring into question previous recommendations to use hills of 3 degrees downhill slope for this form of overspeed training.
Statistical guidelines and expert statements are now available to assist in the analysis and reporting of studies in some biomedical disciplines. We present here a more progressive resource for sample-based studies, meta-analyses, and case studies in sports medicine and exercise science. We offer forthright advice on the following controversial or novel issues: using precision of estimation for inferences about population effects in preference to null-hypothesis testing, which is inadequate for assessing clinical or practical importance; justifying sample size via acceptable precision or confidence for clinical decisions rather than via adequate power for statistical significance; showing SD rather than SEM, to better communicate the magnitude of differences in means and nonuniformity of error; avoiding purely nonparametric analyses, which cannot provide inferences about magnitude and are unnecessary; using regression statistics in validity studies, in preference to the impractical and biased limits of agreement; making greater use of qualitative methods to enrich sample-based quantitative projects; and seeking ethics approval for public access to the depersonalized raw data of a study, to address the need for more scrutiny of research and better meta-analyses. Advice on less contentious issues includes the following: using covariates in linear models to adjust for confounders, to account for individual differences, and to identify potential mechanisms of an effect; using log transformation to deal with nonuniformity of effects and error; identifying and deleting outliers; presenting descriptive, effect, and inferential statistics in appropriate formats; and contending with bias arising from problems with sampling, assignment, blinding, measurement error, and researchers' prejudices. This article should advance the field by stimulating debate, promoting innovative approaches, and serving as a useful checklist for authors, reviewers, and editors.
We twice tested the hypothesis that top running speeds are determined by the amount of force applied to the ground rather than how rapidly limbs are repositioned in the air. First, we compared the mechanics of 33 subjects of different sprinting abilities running at their top speeds on a level treadmill. Second, we compared the mechanics of declined (-6 degrees ) and inclined (+9 degrees ) top-speed treadmill running in five subjects. For both tests, we used a treadmill-mounted force plate to measure the time between stance periods of the same foot (swing time, t(sw)) and the force applied to the running surface at top speed. To obtain the force relevant for speed, the force applied normal to the ground was divided by the weight of the body (W(b)) and averaged over the period of foot-ground contact (F(avge)/W(b)). The top speeds of the 33 subjects who completed the level treadmill protocol spanned a 1.8-fold range from 6.2 to 11.1 m/s. Among these subjects, the regression of F(avge)/W(b) on top speed indicated that this force was 1.26 times greater for a runner with a top speed of 11.1 vs. 6.2 m/s. In contrast, the time taken to swing the limb into position for the next step (t(sw)) did not vary (P = 0.18). Declined and inclined top speeds differed by 1.4-fold (9.96+/-0.3 vs. 7.10+/-0.3 m/s, respectively), with the faster declined top speeds being achieved with mass-specific support forces that were 1.3 times greater (2.30+/- 0.06 vs. 1.76+/-0.04 F(avge)/ W(b)) and minimum t(sw) that were similar (+8%). We conclude that human runners reach faster top speeds not by repositioning their limbs more rapidly in the air, but by applying greater support forces to the ground.
We studied the specificity of elastic-cord towing by measuring selected kinematics of the acceleration phase of sprinting. Nine collegiate sprinters ran two 20-m maximal sprints (MSs) and towed sprints (TSs) that were recorded on high-speed video (180 Hz). Sagittal plane kinematics of a 4-segment model of the right side of the body were digitized for a complete stride at the 15-m point for the fastest trial. Significant (p < 0.001) differences were observed for horizontal velocity of the center of mass (CoM), stride length (SL), and horizontal distance from the CoM of the foot to the CoM of the body. There was no significant difference in stride rate between the MS and TS conditions. Omega-squared analysis showed that elastic-cord towing accounted for most of the variance in acute changes in horizontal velocity (73%), SL (68%), and horizontal position of the CoM at foot contact (64%). Elastic-cord tow training resulted in significant acute changes in sprint kinematics in the acceleration phase of an MS that do not appear to be sprint specific. More research is needed on the specificity of TS training and long-term effects on sprinting performance.
The purpose of this study was to characterize sprint patterns of rugby union players during competition. Velocity profiles (60 m) of 28 rugby players were initially established in testing from standing, walking, jogging, and striding starts. During competition, the individual sprinting patterns of 17 rugby players were determined from video by using the individual velocity profiles. Forwards commenced sprints from a standing start most frequently (41%), whereas backs sprinted from standing (29%), walking (29%), jogging (29%), and occasionally striding (13%) starts. Forwards and backs achieved speeds in excess of 90% maximal velocity (Vmax) on 5 +/- 4 and 9 +/- 4 occasions ( approximately 50% of the sprints performed), respectively, during competition. The higher frequency of sprinting for the backs compared with the forwards highlights the importance of speed training for this positional group. The similar relative distribution of velocities achieved during competition for forwards and backs suggests both positional groups should train acceleration and Vmax qualities. The backs should have a higher total volume of sprint training. Sprinting efforts should be performed from a variety of starting speeds to mimic the movement patterns of competition.
The aim of this study was to examine the effects of sprint running training on sloping surfaces (3 degrees ) on selected kinematic and physiological variables. Thirty-five sport and physical education students were randomized into 4 training groups (uphill-downhill, downhill, uphill, and horizontal) and a control group, with 7 participants in each group. Pre- and posttraining tests were performed to examine the effects of 6 weeks of training on the maximum running speed at 35 m, step rate, step length, step time, contact time, eccentric and concentric phase of contact time, flight time, selected posture characteristics of the step cycle, and peak anaerobic power performance. Maximum running speed and step rate were increased significantly (p < 0.05) in a 35-m running test after training by 0.29 m.s(-1) (3.5%) and 0.14 Hz (3.4%) for the combined uphill-downhill group and by 0.09 m.s(-1) (1.1%) and 0.03 Hz (2.4%) for the downhill group, whereas flight time shortened only for the combined uphill-downhill training group by 6 milliseconds (4.3%). There were no significant changes in the horizontal and control groups. Overall, the posture characteristics and the peak anaerobic power performance did not change with training. It can be suggested that the novel combined uphill-downhill training method is significantly more effective in improving the maximum running velocity at 35 m and the associated horizontal kinematic characteristics of sprint running than the other training methods are.
Optimal elastic cord assistance for sprinting in collegiate women soccer players
- J A Bartolini
- Brown
- Le
- J W Coburn
- Judelson
- Da
- Spiering
- Ba
- N W Aguirre
Bartolini, JA, Brown, LE, Coburn, JW, Judelson, DA, Spiering, BA,
Aguirre, NW, et al. Optimal elastic cord assistance for sprinting in
collegiate women soccer players. J Strength Cond Res 25: 1263-1270,
2011.
Biomechanical characteristics of sprint running during maximal and supra-maximal speed
- Bosco
Bosco, C and Vittori, C. Biomechanical characteristics of sprint
running during maximal and supra-maximal speed. IAAF New
Studies Athletics 1: 39-45, 1986.
Effects of supramaximal running on stride frequency and stride length in sprinters
- Sugiura
Sugiura, Y and Aoki, J. Effects of supramaximal running on stride
frequency and stride length in sprinters. Adv Exer Sports Phys 14: 9-17, 2008.