In the second article of this series on the Bondarchuk principles and soccer training, special development exercises (SDE) are the topic of interest. Special development exercises follow special preparation exercises in the categorisation of exercise complexes leading to sports form. Within this article, the available evidence will be evaluated to maximize SDE by scrutinizing how they are prescribed within training programmes.
Special development exercises are defined by the characteristic that training movements will mimic either form or function, but not both (Bondarchuk, 2007). There are a range of critical and defining movements within soccer performances, one of the most important being running speed (Di Salvo et al, 2007). Running speed, be it acceleration, transition or maximal running speed is important to soccer players (Carling, Le Gall & Dupont, 2012) and various expressions of speed are important features within successful performances. If Bondarchuk’s principles are applied to linear speed, then the selected exercise should resemble the kinematics of the movement using different muscle actions or varying applications of force.
One such type of exercise that is trained to enhance linear speed is resisted running. Resisted running usually requires the athlete to perform a running action against external resistance which typically elicits decreased running velocities and increased ground reaction forces (Martinez-Valencia et al, 2015). The external resistance can be provided by bungees or bands but it is most commonly and efficiently provided by sled towing. Currently there is uncertainty within the available research as to what load is optimal for resisted running so it is worth evaluating the evidence and different stances on this topic.
Lockie, Murphy and Spinks (2003) made a recommendation from their research on resisted running, suggesting that sled loads should be light and should not reduce running velocity to below 90% of maximal speed over a given distance. Changes in shoulder kinematics when using heavier sled loads were of concern to these researchers as such changes in running kinematics were thought to have poor transfer to running performance. Other researchers have taken this notion on board for example, Alcarez, Palao and Elvira (2009) recommend that loads of 7-10% body mass are optimal as this allows the athlete to maintain a high running velocity. The stance that lower loads are optimal is credible on the basis that kinematic parameters are maintained however, there are other kinetic variables that cannot be maximized under low resisting loads. It is also worth considering that SDE do not require form and function simultaneously therefore deviation away from normal running mechanics is not essential.
Other studies have looked at selecting sled loads that maximize propulsive forces and power. For example, Monte, Nardello and Zamparo (2017) observed a plateau in horizontal forces between 20-40% body mass as opposed to unloaded and 15% over 20-meters. In line with this, a significant peak in horizontal power was observed when towing the sled with 20% body mass. The loads used in this study are greater than those discussed above and it appears that there is a trade-off in force expression and velocity of movement resulting in optimal loads to elicit power. Even heavier loads are deemed optimal by Cross, Brughelli, Samozino, Brown and Morin (2017) who used loads between 20-120% body mass incrementing by 10%. Cross et al (2017) compared peak power at each load between sprinters and mixed sport athletes; using a regression model, that accounted for force and velocity, the researchers calculated 82% and 78% for sprinters and track athletes respectively. When analysing rate of force development (RFD) Martinez-Valencia et al (2015) found that 20% body mass optimized the expression of this metric although this was the heaviest load used so it is unclear if heavier loads would have elicited greater RFD. These studies highlight that a wide range of sled loads optimize different kinetic parameters suggesting that loads should be individualized to maximize adaptations that transfer to running performance.
Other acceleration-specific studies have observed resisted sprint starts and it appears that heavier loads maximize force producing capabilities. For example, Cottle, Carlson and Lawrence (2014) found that 20% body mass loads elicited significantly greater impulse during the first step of a crouch sprint start in comparison to 10% body mass and unloaded conditions. Kawamori, Newton and Nosaka (2018) also observed that 30% body mass loads maximized propulsive forces including propulsive impulse and net horizontal impulse during the second step of acceleration in comparison to 10% body mass and unloaded conditions. Such studies example how exercise form can be maintained and function can be manipulated by increasing the amount of time that force is applied for thus, increasing the total impulse.
Within training programmes resisted running with the loads discussed above has had positive effects on athlete running velocity. West et al (2013) demonstrated that resisted running training and traditional sprint training enhanced 10- and 30-metre sprint times, using loads of 12.6% body mass in comparison to traditional training alone amongst professional rugby players. In a more diverse study, Bachero-Mena and Gonzalez-Badillo (2014) compared training groups using 5, 12.5 and 20% body mass in a resisted running programme over seven weeks. The higher load group observed significant improvements in twenty and forty metre sprint times whereas the lower loaded groups achieved significant increases in transition times (20-30 and 10-40m). This evidence demonstrates that heavier loads may have greatest transfer to acceleration, where force is applied over a longer time and light-to-moderate loads enhance maximal velocity running as the athlete is trying to maintain velocity while applying high ground reaction forces.
Interestingly, in systematic review, Petrokas, Morin and Egan (2016) suggest that a range of loads can enhance running velocity although little investigation has been made in to the use of very-heavy loads. In a pilot study Morin (2017) compared two training groups that performed a simple sprint protocol twice weekly; one group was unloaded and the other used eighty-percent body mass sled load. The sled training group noted superior improvements in kinetic measures and sprint times namely, moderate increases in peak force and RFD max over a 30-metre sprint. While this study may suggest that heavy loads are favourable, with no intermediate load to compare with, it is difficult to understand how significant that improvement is.
This article has tried to evidence that resisted running can increase aspects of unresisted running performance and have a positive transfer to soccer. Within the confines of the SDE category resisted running includes a difference in form and function. In consideration of this, running kinematics and velocity need not necessarily be maintained to have a positive transfer to performance. It appears that using loads between 10-40% body mass will not have a negative effect on performance but heavier loads will favour acceleration performance and lighter loads will enhance transition and maximal speed.
References
Alcarez, P. E., Palao, J. M., & Elvira, J. L. (2009). Determining the optimal load for resisted sprint training with sled towing. Journal of Strength and Conditioning Research, 23, 480-485.
Bachero-Mena, B., & Gonzalez-Badillo, J. J. (2014). Effects of resisted sprint training on acceleration with three different loads accounting to 5, 12.5 and 20% of body mass. Journal of Strength and Conditioning Research, 28, 2945-2960.
Bondarchuk. A. (2007). Transfer of training in sports. Michigan, USA: Ultimate Athlete Concepts.
Carling, C., Le Gall, F., & Dupont, G. (2012). Analysis of repeated high-intensity running performance in professional soccer. Journal of Sport Sciences, 30, 325-3356.
Cottle, C. A., Carlson, L.A., & Lawrence, M. A. (2014). Effects of sled towing on sprint starts. Journal of Strength and Conditioning Research, 28, 1241-1245.
Cross, M., Brughelli, M., Samozino, P., Brown, S. R., and Morin, J-B. (2017). Optimal loading for maximizing power during sled-resisted sprinting. International Journal of Sports Physiology and Performance, 12, 1069-1077.
Di Salvo, V., Baron, R., Tschan, H., Calderon Montero, F. J., Bachl, N., & Pigozzi, F. (2007). Performance characteristics according to playing position in elite soccer. International Journal of Sports Medicine, 28, 222-227.
Kawamori, N., Newton, R., & Nosaka, K. (2014). Effects of weighted sled towing on ground reaction force during the acceleration phase of sprint running. Journal of Sports Sciences, 32, 1139-1145.
Lockie, R. G., Murphy, A. J., & Spinks, C. D. (2003). Effects of resisted sled towing on sprint kinematics in field sport athletes. Journal of Strength and Conditioning Research, 17, 760-767.
Martinez-Valencia, M. A., Romer-Arenas, S., Elvira, L. J., Gonzalez-Rave, J. M., Navarro-Valdivielso, F., Alcaraz, P. E. (2015). Effects of sled towing on peak force, rate of force development and sprint performance during the acceleration phase. Journal of Human Kinetics, 46, 139-148.
Monte, A., Nardello, F., & Zamparo, P. (2017). Sled towing: the optimal overload for peak power production. International journal of sports physiology and performance, 12, 1052-1058.
Morin, J-B., Petrokas, G., Jiminez-Reyez, R., Brown, S. R., Samozino, P., & Cross, M. R. (2017). Very-heavy sled training for improving horizontal-force output in soccer players. International Journal of Sports Physiology and Performance, 12, 840-844.
Petrokas, G., Morin, J-B., & Egan, B. (2016). Resisted sled sprint training to improve sprint performance: a systematic review. Sports Medicine, 46, 381-400.
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