The purpose of this study was to clarify effect of uphill sprinting to running spatiotemporal variables and lower limb muscle activity. Twelve university sprinters (seven males) were volunteered to this study. Subjects performed 60 m sprint with maximal effort in two conditions (level sprint vs uphill sprint). Then, we obtained running spatiotemporal variables and electromyography (EMG) from lower limb muscles (biceps femoris, rectus femoris, tibial anterior, lateral head of gastrocnemius). We calculated the running spatiotemporal variables (e.g., running speed, step frequency, step length), EMG activity amplitudes (%MVC), and relative EMG timings in running cycle (%) in analysis section (40-60m). We observed running speed, step frequency, and step length were significantly decreased in the uphill sprint. However, no significant differences were observed in EMG activity amplitudes between two conditions. On the other hand, the onset and offset timings of rectus femoris muscle were significantly shifted to the latter half of the running cycle in the uphill sprint. Therefore, we may consider the possibility that delay in the timing of the recovery movement (i.e., hip flexion) of the swing leg in the uphill sprint. These results suggest that uphill sprint training may affect the timing of muscle activity rather than the amount of muscle activity. We conclude that neuromuscular control of the lower limb muscle is different between uphill sprint and level sprint.

PURPOSE: The purpose of this study was to investigate the relationship between spatiotemporal variables and the muscle activity of the rectus femoris (RF) and biceps femoris (BF) in both legs at various running speeds. METHODS: Eighteen well-trained male athletes (age: 20.7 ± 1.8 yrs) were asked to run for 50 m with 7 different "Subjective Efforts (SEs)" (20 %, 40 %, 60 %, 80 %, 90 %, 95 %, and 100 % SE). SE scaled relative to the maximal effort running (100 %). The spatiotemporal variables (running speed, step frequency, step length) were measured over the distance from 30 m to 50 m. The RF and BF muscle activities were obtained from both legs with wireless electromyography (EMG) sensors. We calculated RF and BF onset/offset timings in both legs (e.g., ipsilateral leg RF is "iRF", contralateral leg BF is "cBF"), which were expressed as % of a running cycle. Based on those timings, we obtained the EMG timing variables (%), as Switch1(iBF-offset to iRF-onset), Switch2 (iRF-offset to iBF-onset), Scissors1 (cBF-onset to iRF-onset), and Scissors2 (iRF-offset to cBF-offset). RESULTS: Running speed was well correlated with the SE, and higher running speed (> 9 m·s-1) was achieved with higher step frequency (> 4.0 Hz). Relative timings of RF and BF onset/offset (%) appeared earlier and later, respectively, with an increase in running speed. The absolute duration of RF activation (sec) was elongated with the decrease in absolute running cycle time (increase in running speed). Both Switch and Scissors showed significant negative correlations with running speed and step frequency. CONCLUSIONS: RF and BF excitation in both legs, as evidenced by changes in both Switch and Scissors, is coordinated for controlling running speed as well as step frequency.

PURPOSE: We aimed to examine the timing of electromyography activity of the rectus femoris (RF) and biceps femoris (BF) in both legs, as well as spatiotemporal variables (running speed (RS), step frequency (SF), step length (SL)) between the maximal speed (Max) phase (50-70 m) and the deceleration (Dec) phase (80-100 m) of the 100-m dash. METHODS: Nine track and field athletes performed the 100-m dash with maximal effort. Spatiotemporal variables of each 10-m section were measured. A portable wireless data logger was attached to the subject's lower back to record electromyographies. We calculated onset/offset timing (%) of RF and BF in both legs using a Teager-Kaiser Energy Operator filter (e.g., ipsilateral leg RF onset is "iRF-onset," contralateral leg BF onset is "cBF-onset") in a running cycle. RESULTS: The decreased RS in the Dec phase (P < 0.001) was due to a decreased SF (P < 0.001). Moreover, iRF-onset (P = 0.002), iRF-offset (P = 0.008), iBF-offset (P = 0.049), and cBF-offset (P = 0.017) in the Dec phase lagged in the running cycle as compared with the Max phase. Furthermore, the time difference between the swing leg RF activity (iRF-onset) and the contact leg BF activity (cBF-onset; "Scissors1") became bigger in the Dec phase (P = 0.041). Significant negative correlations were found between ΔiRF-onset and ΔSF (P = 0.045), and between ΔiBF-offset and ΔSF (P = 0.036). CONCLUSIONS: The decreased RS and SF in the Dec phase of the 100-m dash would be the delayed timing of the RF and BF activities in the same leg as well as the disturbed interleg muscular coordination.

Purpose: Purpose of this study was to elucidate the differences in sprint performance between two different conditions in the 60 m dash: subjects ran alone (Alone Condition: AC) or two runners competed side-by-side (Competitive Condition: CC). Methods: Subjects were twenty-six male university sprinters. They were asked to perform two 60 m dash, the AC and CC, with maximal effort from crouching start. Running spatiotemporal variables were obtained from video images taken with two digital high-speed cameras. Results: Running speed (AC: 9.34 ± 0.45 ms-1 vs CC: 9.40 ± 0.43 ms-1, p = .011) and step length (AC: 2.04 ± 0.12 m vs CC: 2.06 ± 0.10 m, p = .021) in the maximal speed section (30-60m) were significantly increased in the CC. However, there was no significant difference in step frequency (AC: 4.58 ± 0.26 Hz vs CC: 4.57 ± 0.27 Hz, p = .595). There was no significant difference in any variables in the acceleration section (0-30m). Conclusion: These results indicate that running with a competitor improves running speed with increasing step length in the maximal speed section but does not affect performance in the acceleration section. We concluded that competition improves sprint performances in the maximal speed section.

The purpose of this study was to investigate the differences in sprinting movement between children with high and low sprinting ability by using observational evaluation. We analyzed the maximum sprinting speed and sprinting movements of 252 children in the 1st, the 2nd and the 3rd grades of a kindergarten, based on age group and sprinting speed. The main results were as follows:<br>
1. Analysis of variance of sprinting movement scores based on age group and sprinting speed showed that the scores for 3rd grade children were higher than those for 1st and 2nd grade children, and the scores for the groups with medium and high sprinting speed tended to be higher than those for the group with low sprinting speed. This indicates that, although rational sprinting movement can be acquired with increasing age, the better the sprinting ability of children, the more rational the sprinting movement that is acquired.<br>
2. The results for each of the evaluation items suggested that the acquisition of rational sprinting movement progressed to a certain degree with age in the “forward swing range of the elbows”, the “timing of the scissorslike leg motion” and the “foot contact aspect”. However, because some previous studies have indicated that the foot contact aspect may be affected by the overall movement of the lower limb, older children may not necessarily learn to acquire contact on the midfoot or forefoot.<br>
3. While it is expected that the subjects would become more proficient in the “flexion and extension of the elbows” and the “range of the leg motion” with increasing age, the differences among the sprinting speed groups were significant, suggesting that remaining unskilled movements may be a factor in decreasing sprinting speed regardless of age.<br>
These results suggest that the acquisition of basic movement patterns and refinement toward more purposeful movements in sprinting occur simultaneously in early childhood, and that the complex aspect of proficiency is a characteristic feature of infants' sprinting movements.

PURPOSE: The purpose of this study was to investigate the relationship between spatiotemporal variables of running and onset/offset timing of rectus femoris (RF) and biceps femoris (BF) muscle activities in both legs. METHODS: Eighteen male well-trained athletes (age = 20.7 ± 1.8 yr) were asked to run 50 m at maximal speed. The spatiotemporal variables (running speed, step frequency, and step length) over the distance from 30 to 50 m were measured. In addition, RF and BF muscle activities were obtained from both legs using wireless EMG sensors. To quantify the onset and offset timing of muscle activity, the band-pass filtered (20-450 Hz) EMG signal was processed using a Teager-Kaiser energy operator filter. We calculated RF and BF onset/offset timings (%) in both legs (e.g., ipsilateral leg RF [iRF] and contralateral leg BF [cBF]) during running cycle. Based on those timings, we obtained the EMG timing variables (%) as follows: "Switch1 (iBF-offset to iRF-onset)," "Switch2 (iRF-offset to iBF-onset)," "Scissors1 (cBF-onset to iRF-onset)," and "Scissors2 (iRF-offset to cBF-offset). RESULTS: We found that "Switch2" had positive (r = 0.495, P = 0.037), "Scissors1" had negative (r = -0.469, P = 0.049), and "Scissors2" had positive (r = 0.574, P = 0.013) correlations with step frequency. However, these variables had no significant correlations with running speed or step length. CONCLUSIONS: These results indicate that higher step frequency would be achieved by smoother switching of the agonist-antagonist muscle activities and earlier iRF activation relative to the cBF activity. To improve sprint performance, athletes and coaches should consider not only muscle activities in one leg but also coordination of muscle activities in both legs.

The effect of the different training regimes and histories on the spatiotemporal characteristics of human running was evaluated in four groups of subjects who had different histories of engagement in running-specific training; sprinters, distance runners, active athletes, and sedentary individuals. Subjects ran at a variety of velocities, ranging from slowest to fastest, over 30 trials in a random order. Group averages of maximal running velocities, ranked from fastest to slowest, were: sprinters, distance runners, active athletes, and sedentary individuals. The velocity-cadence-step length (V-C-S) relationship, made by plotting step length against cadence at each velocity tested, was analyzed with the segmented regression method, utilizing two regression lines. In all subject groups, there was a critical velocity, defined as the inflection point, in the relationship. In the velocity ranges below and above the inflection point (slower and faster velocity ranges), velocity was modulated primarily by altering step length and by altering cadence, respectively. This pattern was commonly observed in all four groups, not only in sprinters and distance runners, as has already been reported, but also in active athletes and sedentary individuals. This pattern may reflect an energy saving strategy. When the data from all groups were combined, there were significant correlations between maximal running velocity and both running velocity and step length at the inflection point. In spite of the wide variety of athletic experience of the subjects, as well as their maximum running velocities, the inflection point appeared at a similar cadence (3.0 ± 0.2 steps/s) and at a similar relative velocity (65-70%Vmax). These results imply that the influence of running-specific training on the inflection point is minimal.

Purpose. This study investigated the relationship between subjective effort (SE) and kinematics/kinetics throughout an entire 50 m sprint. Methods. Fifteen male sprinters performed the 50 m sprint at 3 different levels of SE (100 %SE; maximal-effort, 90 %SE and 80 %SE, sub-maximal efforts). Kinematic and kinetic data were obtained with a digital high speed camera and 50 ground reaction force (GRF) plates placed every 1 m in the running lane. Variables recorded were sprint time, running speed, step frequency, step length, aerial time, contact time, GRF, and ground reaction impulse (GRI). Results & Discussion. Sprint times decreased with increases in SE. However, some subjects ran their fastest 50m at a sub-maximal SE. Thus, the optimal combination of step length & frequency necessary for obtaining maximum speed does not necessarily occur at maximal SE. Indeed, while step frequency significantly increased with an increase in SE, step length was usually the longest at a sub-maximal SE. The vertical GRI in the first half of the ground contact period was significantly greater at sub-maximal SEs. Vertical GRIs and horizontal GRIs in the second half of the ground contact period did not significantly differ among different SEs. Our results suggest that those runners who increase SF too much at maximal SE do so at the cost of decreasing step length (SL). Thus, applying a large force against the ground in the first half of the ground contact period would be effective for improving step length.

This study was performed to devise an instructional program for children who were not good at sprinting and to verify the program's effectiveness for improvement of sprinting ability and motion.<br> The participants were 19 upper grade elementary school children who were not good at sprinting. The program included 2 drills with some teaching devices and running on flat markers. The children attended the program for 8 days (2 days per week) and each lesson lasted an hour. In order to validate the program outcome, sprint time (50 m), interval speed (every 10 m), average speed, maximal speed, rate of speed decline, interval and average step frequency and step length were analyzed, and sprint motions were evaluated. The results were as follows:<br> 1) Most of the children's 50 m times were below the national average. This suggested that their negative feelings toward sprinting resulted from the realization that they were unable to run as fast as other children.<br> 2) The children's sprint times were improved after the program, and a significant correlation between pre-time and post-pre time was revealed. It was also found that the greater the increase in the children's step frequency, the faster their sprint times became. These results suggest that sprinting instruction allows low-performing children to increase their step frequency and improve their sprint times.<br> 3) The main aim of the program was to improve children's sprint motions in the mid sprint phase, and the participants practiced start motions only twice during the program. As a result, speeds from the start to 10 m, 20-50 m, and maximum speed were increased significantly by this practice, suggesting that significant changes of speed led to improvement of the sprint times.<br> 4) Participants became able to swing back their leg under their body and to make contact with the ground with the middle or front of the foot. Therefore it was considered that the drills and running on flat markers with teaching devices were valuable for improving the children's sprint motions.<br> 5) Although the scissors-like leg motion was not improved by practice with a color board and bells, the kneefolding motion of the swing leg did appear to be improved. Therefore, the children seemed to acquire basic skill in more rapid scissors-like leg motion.<br> These results suggest that our instructional program was effective in enabling children to improve their sprinting ability and motion. However, additional research focusing on aspects such as the relationship between sprinting ability and sprint motion, or individual feelings and motor competency in the context of sprinting, will be needed.