Milan Čoh

Dynamic factors and electromyographic activity in a sprint start

The aim of the study was to establish the major dynamic parameters as well as the EMG activation of muscles in a sprint start as the first derivative of sprint velocity. The subject of the analysis was block velocity, the production of force in the front and rear starting blocks, the block acceleration in the first two steps and the electromyographic activity (EMG) of the following muscles: the erector spinae muscle, gluteus maximus muscle, rectus femoris muscle, vastus medialis muscle, vastus lateralis muscle, biceps femoris muscle and gastrocnemius–medialis muscle. One international-class female sprinter participated in the experiment. She performed eight starts in constant laboratory conditions. The 3-D kinematic analysis was made using a system of nine Smart-e 600 cameras operating at a frame rate of 60 Hz. Dynamic parameters were established by means of two separate force platforms to which the starting blocks were fixed. A 16-channel electromyograph was used to analyse electromyographic activity (EMG). It was established that the block velocity depended on the absolute force produced in the front and rear starting blocks and that it was 2.84±0.21 m.s -1 . The maximal force on the rear and front blocks was 628±34 N and 1023±30 N, respectively. In view of the total impulse (210±11 Ns) the force production/time ratio in the rear and front blocks was 34%:66%. The erector spinae muscle, vastus lateralis muscle and gastrocnemius–medialis muscle generate the efficiency of the start. The block acceleration in the first two steps primarily depends on the activation of the gluteus maximus muscle, rectus femoris muscle, biceps femoris muscle and gastrocnemius–medialis muscle. A sprint start is a complex motor stereotype requiring a high degree of integration of the processes of central movement regulation and an optimal level of biomotor abilities. (Biol.Sport 26:137-147, 2009)

Differences between the elite and subelite sprinters in kinematic and dynamic determinations of countermovement jump and drop jump.

Abstract Čoh, M and Mackala, K. Differences between the elite and subelite sprinters in kinematic and dynamic determinations of countermovement jump and drop jump. J Strength Cond Res 27(11): 3021–3027, 2013—The aim of this study was to examine the relationship between selected variables of lower extremities explosive power measured via countermovement jump (CMJ) and drop jump (DJ) and sprinting ability over 60- and 100-m dash. Twelve national-level Slovenian sprinters were assigned to 2 groups: elite (n = 6) and subelite (n = 6). The grouping criterion was performance in 60 and 100 m in official competition. Biomechanical parameters of both jumps were measured with the use of bipedal force platform and a system of 9 infraspectral charge-coupled device (CCD) cameras with a 200 Hz frequency. Differences between the groups of sprinters were examined with the use of repeated-measures analysis of variance. In CMJ, the differences (p < 0.05) between the groups were revealed in take off velocity (elites = 3.23 m·s−1, subelites = 2.94 m·s−1), height of the jump, vertical velocity of body center of gravity, and the impulse of force in the concentric phase of the jump (concentric impulse: elites = 123.91 N·s; subelites = 108.06 N·s). In the DJ, elite and subelite sprinters differentiated in the realization of movement velocity in the eccentric and concentric phases (take off velocity: elites = 3.18 m·s−1, subelites = 2.87 m·s−1; eccentric velocity: elites = 3.05 m·s−1, subelites = 2.81 m·s−1). This investigation provides evidence that vertical jumps and DJs are very important tools to meet the demands of sprint training according eccentric-concentric muscular work. The DJ showed better quality than CMJ in the neuromuscular specificity.

Biomechanical analysis of squat jump and countermovement jump from varying starting positions.

Abstract Mackala, K, Stodółka, J, Siemienski, A, and Ćoh, M. Biomechanical analysis of squat jump and countermovement jump from varying starting positions. J Strength Cond Res 27(10): 2650–2661, 2013—The purpose of this study was to investigate the effect of 2 strategies, defined by foot placement during the initiation of the take-off on performance in vertical jumps. The additional area of interest in this experiment was whether technique of the take-off phase might be an exploratory factor that has different electromyogram (EMG) muscle activity during squat jump (SJ) and countermovement jump (CMJ) performed starting from the standard position, with parallel foot placement, and from the experimental one, with straddle foot placement. Six well-experienced male 100–400 m sprinters, who were members of the Polish youth and senior national team (mean values: age 21.6 years, best performance: 100 m in 10.54 seconds and 400 m in 45.54 seconds), performed vertical SJ and vertical CMJ from 2 initial positions with different foot placement. To collect all selected kinematic and kinetic data, the video recording system BTS Vixta was used in conjunction with force platforms (Kistler model 9286B). The latest system for 3D motion analysis, BTS SMART, based on the passive IR reflective markers was also applied. Electromyograms of 6 lower limb muscles were collected using a Noraxon EMG device. The CMJ was on average 7 cm higher than the SJ (CMJ, 85 cm and SJ, 78 cm), which amounts to 8.97%. This was not because of the increase of center of gravity (COG) velocity at take-off because velocities of center of gravity (COG) projection were almost equal (SJ, 2.93 m·s−1compared with CMJ, 2.99 m·s−1). No significant differences of both magnitude and rate of development of the muscle torques and powers between jumps were found, but when we analyzed the problem with division into single legs (right and left) and with division into different jumps (SJ and CMJ), the differences were evident. The profiles of EMG activity of selected muscles showed some differences between SJ and CMJ. The vertical SJ and CMJ performance measurement may be of value to coaches and conditioning specialists who wish to develop or assess the power ability of lower extremities either unilaterally (single leg) or bilaterally (sum of both legs).

Biomechanical analysis of standing long jump from varying starting positions.

Abstract Mackala, K, Stodółka, J, Siemienski, A, and Ćoh, M. Biomechanical analysis of standing long jump from varying starting positions. J Strength Cond Res 27(10): 2674–2684, 2013—The purpose of this study was (a) to investigate the effect of the different foot movement (placement) during take-off and the initial knee joint angle used in standing long jump by the ground reaction forces analysis and 3-dimensional motion analysis (BTS SMART motion) and (b) investigate how the jump performances of different foot placement is related to the electromyography (EMG) activity (Noraxon) of 3 selected muscle groups (m. gastrocnemius, m. gluteus maximus, m. rectus femoris, m. tibialis anterior, m. biceps femoris, and m. vastus medialis). Six high caliber sprinters (100 m: 10.87 ± 0.38 seconds and 400 m: 46.75 ± 1.05 seconds) performed a series of jumps from parallel and straddle foot placement at take-off on a 2 force platform (Kistler model 9286B) to determine if a different pattern of take-off improves jumping distance. Using kinematic and kinetic data, the knee joint angle, the trajectories of center of mass (COM), magnitude of take-off peak force, and impulse during take-off phase were calculated. Average standing long jump performances with straddle foot placement were 13.58 cm (5.18%) above that from parallel feet placement. The take-off velocity with 90° knee initial angle initiation of take-off was not different (1.18 and 1.17 m·s−1, respectively) between the 2 jumps. The take-off angles on the COM trajectory also showed differences (69.87 and 66.8°, respectively) between each other. The contribution (EMG activation) made by the 6 muscles were almost the same during all phases for the 2 jumps; however, some differences can be found, in either unilateral (single leg) or sums of both legs (bilateral) measurements. A recommendation can be formulated that the contribution of straddle foot placement during take-off can significantly increase the value of power measurement especially when the evaluation requires a complex movement structure with the division on the left and right legs, for example, sprint start from block.

Differences in kinematic parameters of athletes of different running quality

The aim of the study was to determine the differences among subjects of different sprinting quality in the variables of running dynamics in the 100 m sprint event and in the variables of kinematic indicators (stride frequency, stride length, foot-ground contact duration, airborne phase duration). The research was conducted on a sample of 133 physical education teacher male students, aged 19 to 24 years (age 21.7 ± 1.08 yrs ; body height 180.8 ± 6.98 cm ; body mass 76.6 ± 7.62 kg), first year students at the Faculty of Kinesiology, University of Zagreb, who regularly attended their athletics classes. Basic descriptive statistical parameters were computed. Cluster analysis was used to determine sprinting-quality-based homogeneous groups of subjects. The qualitative differences among the subjects pertaining to the defined groups were established by canonical discriminant analysis. One significant discriminant function was obtained differentiating the group of students who performed well from all the other groups of students with poorer sprint performance. The best performance group demonstrated running technique characterised by the shortest foot-ground contact time in the phases of starting acceleration and maximum speed running, and a larger stride length in the phase of maximum speed running.

Biomechanical, Neuro-muscular and Methodical Aspects of Running Speed Development

Biomechanical, Neuro-muscular and Methodical Aspects of Running Speed Development The purpose of present review article is to gather the most important findings in the field of speed development including biomechanical, motor and neuro-muscular factors. Maximum speed is a complex motor ability, which manifests itself in real sports situations and is an important factor in various sports disciplines. Efficiency of maximum running is defined with frequency and the length of stride. Both variables are mutually dependant; they also depend on the processes of central regulation of motor stereotype. From the biomechanical point of view, a running stride as a basic structural unit depends on eccentric-concentric muscular cycle of take-off action. Utilisation of elastic strength in muscular-tendon complex and pre-activation of the gastrocnemius muscle is highly important in this element. Maximum running is very limited hereditary motor ability with characteristic of reduced possibility for controlling movement. Cerebellum, co-activation of muscles in kinetic chain and the frequency of activation of motor units play important roles in controlling the activation of agonists and antagonists. The prime goal of training is to create an optimal model of motor stereotype in the zone of maximum speed. Such process has to be long term and methodical.

Can infrared thermography be used to monitor fatigue during exercise? A case study

Background Infrared thermographic imaging (IRTG) is a safe and reliable technology used to monitor skin temperature. The main aim of our study was to evaluate the relationship between skin temperature changes and muscle fatigue in order to answer the main research question if IRTG can be used to monitor muscle fatigue. Methods This was a case study performed on a 23-year-old trained middle distance runner. After warm-up the subject was exercising on the dynamometer for 7.5 min at 120°/s performing only concentric contractions of quadriceps. At the same time IRTG recording of both (exercising and non-exercising) quadriceps was performed. Results A correlational analysis that was performed in order to quantify the relationship between power and temperature change over time has shown that there is a significant negative correlation between skin temperature increase and power decrease (r = −0.543, p = 0.036) of exercising quadriceps. In linear regression model the exercising quadriceps power could be predicted from skin temperature. No such relationships were noted for the non-exercising limb that served as a control. Conclusion We believe that correlation between skin temperature change and muscle power output as described in this case study deserves further analysis on the larger sample including subjects of the different ages, health status, and physical abilities in order to create a new tool for monitoring the muscle fatigue.

Biomechanical Differences in the Sprint Start Between Faster and Slower High-Level Sprinters

Abstract The purpose of this study was to examine the kinematic and kinetic differences of the sprint start and first two steps between faster and slower high-level sprinters. Twelve male sprinters were dichotomized according to personal best 60- and 100-m times. Each participant performed five starts under constant conditions. An eight-camera system was used for 3-D kinematic analysis. Dynamic forces at the start were determined with starting blocks mounted on bipedal force plates. Measures of front and rear block total force, front and rear block maximal force, time to front and rear block peak force, total force impulse, total horizontal and vertical impulse, front and rear block force impulse, time of block clearance, block leaving velocity and block leaving acceleration were collected. Between-group comparisons were made using independent samples t tests (p < 0.05) and by calculating effect sizes (Cohen’s d). Spearman’s correlation coefficients were used to examine the relationships between sprint start kinematics, kinetic measures and sprint performance. Significant between-group differences were observed in rear block total force (p = 0.0059), rear block maximal vertical force (p = 0.0037) and total force impulse (p = 0.0493). Only front block total force significantly correlated with 100 m sprint performance in both the slower and faster groups (r = 0.94 and 0.54, respectively; p = 0.05). Our findings suggest that faster sprinters show enhanced sprint start motor performance with greater force development than slower sprinters.

Asymmetry of Step Length in Relationship to Leg Strength in 200 meters Sprint of different Performance Levels

Asymmetry of Step Length in Relationship to Leg Strength in 200 meters Sprint of different Performance Levels The purpose of this study was to quantify and compare asymmetry of stride length during 200 m sprint in different levels of performance. Six sprinters from national and regional levels participated in the study. They were assigned to 3 groups: school-boys (novice sprinters) junior (intermediate) and senior (advance - national and regional level) category. This study investigated selected kinematic parameters with special focus on stride length. The resulting values were measurements of each stride length (rounded-off to nearest full centimeter) during a 200 m sprint, using a manual stride measurement method. The findings indicate that the asymmetry of stride length exists in all categories, and the impact on decreasing velocities of the youngest sprinters (school-boys) are significantly associated with shorter strides, whereas cadence has little change. However, when a statistical adjustment was made for each group of runners it was found that more advanced runners did not have a significantly higher level of asymmetry with stride length at any given velocity.

Kinematic Structure at the Early Flight Position in Ski Jumping

The purpose of our research was to establish the variability of correlation between the length of the jumps and selected multi-item kinematic variables (n=9) in the early flight phase technique of ski jumping. This study was conducted on a sample of elite Slovenian ski jumpers (N=29) who participated in the experiment on a jumping hill in Hinterzarten, Germany (HS95m) on the 20th of August, 2008. The highest and most significant correlations (p=0.01) with the length of the ski jump were found in the multi-item variable height of flying, which was also expressed with the highest level of stability of the explained total variance (TV) on the first factor (TV=69.13%). The most important characteristic of the aerodynamic aspect of early flight was the variable angle between the body chord and the horizontal axis with significantly high correlations (p<0.05). The stability of that aerodynamic factor was very high (TV=65.04%). The results were essentially similar for the multi-item variable angle between left leg and the horizontal axis (TV=61.88%). The rest of the multi-item kinematic variables did not have significant correlations with the multi-item variable length of jump. Only two more variables, the angle between the upper body and the horizontal plane (TV=53.69%), and the angle between left ski and left leg (TV=50.13%), had an explained common variance on the first factor greater than 50% of total variance. The results indicated that some kinematic parameters of ski jumping early flight technique were more important for success considering the length of the jump.