Biomechanical Performance Factors in the Track and Field Sprint Start: A Systematic Review.

In athletics sprint events, the block start performance can be fundamental to the outcome of a race. This Systematic Review aims to identify biomechanical factors of critical importance to the block start and subsequent first two steps performance. A systematic search of relevant English-language articles was performed on three scientific databases (PubMed, SPORTDiscus, and Web of Science) to identify peer-reviewed articles published until June 2021. The keywords "Block Start", "Track and Field", "Sprint Running", and "Kinetics and Kinematics" were paired with all possible combinations. Studies reporting biomechanical analysis of the block start and/or first two steps, with track and field sprinters and reporting PB100m were sought for inclusion and analysis. Thirty-six full-text articles were reviewed. Several biomechanical determinants of sprinters have been identified. In the "Set" position, an anthropometry-driven block setting facilitating the hip extension and a rear leg contribution should be encouraged. At the push-off, a rapid extension of both hips and greater force production seems to be important. After block exiting, shorter flight times and greater propulsive forces are the main features of best sprinters. This systematic review emphasizes important findings and recommendations that may be relevant for researchers and coaches. Future research should focus on upper limbs behavior and on the analysis of the training drills used to improve starting performance.

Regional fat mobilization and training type on sedentary, premenopausal overweight and obese women.

OBJECTIVE: Little is known about the influence of different training types on relative fat mobilization with exercise. The purpose of this study was to analyze the changes induced by aerobic training (AT), resistance (RT) or a combination of both (AT+RT) on total fat mass (TFM) and regional fat mass (RFM). Further, the relative contribution of different regions, upper limbs (UL), lower limbs (LL), and trunk (Tr), were compared. DESIGN AND METHODS: Forty-five overweight and premenopausal women were randomized in either AT, RT or AT+RT. All training groups exercised for the same duration (60 min), 3 times per week for 5 months. Body composition was estimated using dual energy X-ray absorptiometry. RESULTS: TFM decreased significantly in all groups (-4.6 ± 1.9 kg; -3.8 ± 2.6 kg, and -4.7 ± 3.0 kg in AT, RT, and AT+RT groups respectively; P < 0.001). The relative contribution of FM into each segment changed significantly: TrFM represented 46.6% ± 5.8% of TFM at baseline and reduced to 43.1% ± 5.5% (P < 0.001); LLFM was 39.7% ± 5.8% vs. 41.6% ± 5.7% (P < 0.01); ULFM was 11.3% ± 1.3% vs. 12.2% ± 1.4% (P < 0.01). CONCLUSION: Training type did not influence changes of TFM and RFM. Fat mobilization came predominantly from Tr in all training protocols. These findings suggest that overweight and obese women can reduce TFM and RFM, independently of training type.

EMG activation of abdominal muscles in the crunch exercise performed with different external loads.

OBJECTIVE: The aim of this study was to describe by means of surface electromyography the activation of the rectus abdominis, obliquus externus and rectus femoris muscles during the "crunch" abdominal exercise performed with loads. METHODS: Thirteen subjects performed crunch exercises with loads representing 80, 60, 40 and 20% of the 1-RM (100%) in a random order with the subjects drawing lots, and with a 5 min rest between sets. Surface bipolar EMG electrodes were used. The root mean square of the EMG was calculated for the first repetition of each load. Differences between conditions were tested using a one way ANOVA for repeated measures. Post-hoc Bonferroni tests was used to detect significant differences between specific loads (p<0.05). RESULTS: An average of the percentage values of all studied abdominal muscles was used as a representative value of abdominal synergy (Ab Syn). In general it can be concluded that the abdominal muscles were significantly more recruited in the 100% load condition. Abdominal activation significantly differed between the various loads; however, in general adjacent loads (20 vs. 40% - 1-RM) did not differ. CONCLUSIONS: These results suggest that for young, healthy and physically active adults when the objective is progression in the training process of abdominal force, the option ought to be for changes of load superior to 20% of the 1-RM.