PEDRO E. ALCARAZ, JOSE ́ MANUELPALAO, JOSE ́ L. L. ELVIRA, AND NICHOLAS P. LINTHORNE
Journal of Strength and Conditioning Research VOLUME 22, NUMBER 2, MARCH 2008
This week’s review focusses on the paper presented by Alcaraz and his associates.
The authors examine resisted sprinting, an important facet of sprint training, which is believed to enhance both acceleration and top speed. The authors compare three different resistive devices; the sled, the parachute, and the weighted belt or vest, paying attention to their effect on the kinematics of maximum speed sprinting.
The objective of loaded sprinting is to place greater load on the muscles used to achieve maximum speed.
The load will decrease the velocity of the athlete. The more the load slows the athlete, the greater the stimulus to adapt. But this decrease in speed should not come at the price of altered kinematics. Based on the work of Lockie, Murphy and Spinks (2003), the authors chose to use a load which decreased the maximum speed of the athlete by no more than 10% as this load would not appreciably change the athlete’s mechanics. The author’s pilot work determined these loads to be 16% body mass on a 3.6 m cord for the sled, the parachute measured 1.2 x 1.2 m 2, and the weight belt was loaded to 9% of the athlete’s weight.
The trials were carried out over 30 m with a 20 m acceleration. Their results indicated that both the parachute and the sled tended to cause the athlete to lean forward slightly but only the sled produced a statistically significant change (p≤0.05). All other kinematic variables did not change significantly (p≤0.05).
The authors emphasise that the effect of resisted sprinting on performance has not been confirmed, the effect is based on anecdotal evidence. To confirm a cause effect relationship, further research is required.
The coach can draw several useful conclusions from this research. The load chosen should not decrease the speed of the athlete by more than 10%. The loads utilised by the authors are a valuable starting point but the exact value should be attained through testing. The SplitFast system can easily provide this data. Simply set the mode of the SplitFast Hub to Flying Start. Then set the first gates mode to Start and the second gates mode to Finish. Place the first gate at the beginning of the top speed zone and the second at the end of the zone. We recommend the athlete be given at least 30 meters to accelerate and the top speed zone should be at least 10 meters long. As the athlete runs through the first gate the timer starts and stops as the athlete passes through the second gate. The time is accurate to one thousandth of a second. The speed of the athlete is given by dividing the distance between the two gates by the time.
The authors also recommend that the sled should be attached to the waist rather than the upper back as this will minimise forward lean of the athlete. They also suggest that, when using a weighted belt or vest, the load should be evenly distributed on the front and back of the body.
We congratulate Alcaraz and his associates for presenting this valuable, practical piece of research and recommend that the reader access the full paper to fully appreciate the work.
Other works cited in the paper.
1. Lockie, RG, Murphy, AJ, and Spinks, CD. Effects of resisted sled towing on sprint kinematics in field-sport athletes. J Strength Cond Res 17:760–767, 2003