[This is a guest post by Nic Shea. Nic is a PhD student in Integrative physiology at Georgia Tech. Nic works in the exercise physiology lab researching hydration and thermoregulation and owns Athlete Physics. Prior to Georgia Tech, Nic finished his master’s degree in exercise physiology at the University of North Carolina. Nic has coached strength and conditioning at collegiate and high school levels and wrestling at the high school level. He holds the NCSA-CSCS and USA Weightlifting-1 certifications. Nic completed his Bachelor’s degree at Truman State University where he wrestled and was a 2x NCAA Academic All-American in 2013 & 2014.]
Explosive force development is a primary attribute that separates phenomenal athletes from good athletes (Kraska, 2009). Injury prevention is an attribute that enables great athletes to become phenomenal athletes, if you’re not injured you can train more than an athlete who is injured. Slowing down the speed outside forces (opponents, balls, etc.) involves eccentric muscle contractions (muscle lengthening) and is measured by rate of force acceptance, which is related to explosive force production (Jeronimo, 2016).
- Rate of Force Production- The force generated in the early part of muscle contraction (0-200ms).
- Rate of Force Acceptance- The rate of slowing down movements.
An eccentric muscle contraction occurs when an athlete is absorbing force. This occurs in running immediately after the foot contacts the ground, in weight training on the descending phase of a squat and other athletic movements including jumping, changing direction and kicking (Mero 1992, Schonfield 2010). Muscle strains are one of the greatest causes of injury and can occur in athletic movements if eccentric contraction is not strong enough 250 milliseconds after limb contact (Bisseling 2006, Knight 1996, Merrick, 2002). In order for eccentric contraction to be effective in injury prevention, an athlete needs to have a high amount of eccentric strength. For instance, an athlete cannot effectively absorb high forces if he/she is not strong in the first place. The nervous system needs to work in combination with the eccentric contractions to control speed and direction of human movement. If the nervous and muscular combination system lose control, there is a greater chance of ligament injuries or sprains (Hewett, 2010).
Maintaining good posture during running, jumping and landing actions not only improves the speed of these movements but also decreases risk for spinal injuries (Griffen 2000, Schache 2002). To maintain good posture during athletic movements the posterior chain muscles and postural muscles need to be
- Activated quickly
Again, related to the statement above, if these muscles are weak it doesn’t matter how fast you activate them because their maximal strength is not strong enough to overcome outside forces.
Agility and Force Acceptance
In sports requiring agility, high external forces are often placed on the knee which can manifest as a meniscus or ACL injury (Hewett 2005). However, if an athlete can maintain a high force acceptance he/she can reapply the external force for faster acceleration due to Newton’s 3rd law of motion (for every action there is an equal and opposite reaction). Again, the athlete needs to be strong in the first place to have a quick force acceptance and receive the acceleration benefits from Newton’s 3rd law (Jeronimo, 2016).
Practitioners could argue that the rate of force acceptance is more important than simply being strong enough to accept the force and therefore, their athletes should train at a weight that allows fast rates of force acceptance (ie. moving light weights fast). This topic has been addressed many times in training studies which have collectively shown training at a heavy weight with the mental intention of moving as fast as possible improves strength and rate of force production and therefore rate of force acceptance capacity. Training with light weights at fast speeds may only improve rate of force production (Cormie 2010, McBride 2002, Conley 2011). That said, if you want to take a well-round training approach, you might consider developing strength with heavier weights and training rate of force acceptance with light weight at fast speeds (Reiser 2006, Jeronimo, 2016). This way the athletes can train the entire force/velocity spectrum.
Explosive strength and rate of force acceptance are closely related and both are important for athletic performance and injury prevention. Strength and more specifically eccentric strength is important to have a high rate of force acceptance. Therefore, to improve rate of force absorption with weaker athletes focus on improving strength first.
- Develop lower body strength (squatting 2x body weight).
- Use medicine balls (15-35% 1RM) to train at fast velocities (Conley, 2011)
- Strengthen the posterior chain (hamstrings, glute muscles, back muscles, calves).
- Practice good posture in running and landing.
- Train using elastic bands and/or emphasis on eccentric contraction (Rhea, 2009)
- Bisseling, R. W., & Hof, A. L. (2006). Handling of impact forces in inverse dynamics. Journal of biomechanics, 39(13), 2438-2444.
- Griffin, L. Y., Agel, J., Albohm, M. J., Arendt, E. A., Dick, R. W., Garrett, W. E., … & Johnson, R. J. (2000). Noncontact anterior cruciate ligament injuries: risk factors and prevention strategies. Journal of the American Academy of Orthopaedic Surgeons, 8(3), 141-150.
- Hewett, T. E., Myer, G. D., Ford, K. R., Heidt, R. S., Colosimo, A. J., McLean, S. G., … & Succop, P. (2005). Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes. The American journal of sports medicine, 33(4), 492-501.
- Jeronimo, L., & Pelot, T. (2016). Rate of Force Acceptance as an injury prevention strategy in athletic populations. Retrieved from http://elitetrack.com/articles/rate-force-acceptance-injury-prevention-strategy-athletic-populations/
- Kraska, J. M., Ramsey, M. W., G. Gregory, H., Nate, F., Sands, W. A., Stone, M. E., & Stone, M. H. (2009). Relationship between strength characteristics and unweighted and weighted vertical jump height. International journal of sports physiology and performance, 4(4), 461-473.
- McBride, J. M., Triplett-McBride, T., Davie, A., & Newton, R. U. (2002). The effect of heavy-vs. light-load jump squats on the development of strength, power, and speed. The Journal of Strength & Conditioning Research, 16(1), 75-82.
- Merrick, M. A. (2002). Secondary injury after musculoskeletal trauma: a review and update. Journal of athletic training, 37(2), 209.
- Mero, A., Komi, P. V., & Gregor, R. J. (1992). Biomechanics of sprint running. A review. Sports medicine, 13(6), 376-392.
- Prue, P., McGuigan, M. R., & Newton, R. U. (2010). Influence of Strength on the Magnitude & Mechanisms of Adaptation to Power Training. Med Sci Sports Exerc, 42(8), 1566-1581.
- Reiser II, R. F., Rocheford, E. C., & Armstrong, C. J. (2006). Building a better understanding of basic mechanical principles through analysis of the vertical jump. Strength and Conditioning Journal, 28(4), 70.
- Rhea, M. R., Kenn, J. G., & Dermody, B. M. (2009). Alterations in speed of squat movement and the use of accommodated resistance among college athletes training for power. The Journal of Strength & Conditioning Research, 23(9), 2645-2650.
- Schache, A. G., Blanch, P., Rath, D., Wrigley, T., & Bennell, K. (2002). Three-dimensional angular kinematics of the lumbar spine and pelvis during running. Human movement science, 21(2), 273-293.
- Schoenfeld, B. J. (2010). Squatting kinematics and kinetics and their application to exercise performance. The Journal of Strength & Conditioning Research, 24(12), 3497-3506.
- Steinagel, M. C. (1996). Cryotherapy in Sport Injury Management. Journal of athletic training, 31(3), 277
- Conley, M. S., & Stone, M. H. (2011). ACSM Current Comment: Explosive Exercise. Retrieved January 15, 2018, from http://www.hydragym.com/research/ExplosiveExerciseTraining.pdf.