Task Specificity on Rate of Force Development and Joint Angles for Better Transfer

 By Daniel Cobian, MS, CSCS, RSCC*D, CES

Sports conditioning program design involves the aim of enhancing performance with considerations to the movements that govern the specific sport.  Baseball performance relies on quick and powerful movements at higher velocities needed for sprinting, pitching, and swinging a bat, rather than movements that depend on maximal strength efforts that may have more of an influence in American football for example.  Acknowledging that the time needed to generate maximal contractions takes at least 300-ms, while many sports activities only require 0 to 200-ms, may help develop a rationale during program design^{2, 4}).  Therefore, when programming for a power-based sport such as baseball, the rate of force development (RFD) needs consideration as a means to address task specificity through neuromuscular mechanisms that may serve as an opportunity for a greater degree of transfer.  In addition, training with variations in joint-angles in exercises such as the squat, may alter biomechanical measures associated with task specificity, which may also affect RFD. 

To address the influences of the specificity of training, Tillin and Folland compared the effects of short-term maximal versus explosive strength training on maximal and explosive force generation, while assessing their neuromuscular mechanisms⁴.  The participants included 19-recreationally trained males with a mean age of 20.9-years who completed four weeks of maximal strength training (MST) or explosive strength training (EST).  The MST training group were instructed to progressively contract up to 75% of maximal voluntary force (MVF) and hold for three seconds, while the EST group was instructed to contract as fast and as hard as possible for approximately 1-sec.  Electromyography (EMG) data were collected via surface electrodes placed over the rectus femoris, vastas, lateralis, and vastas medialis, while force recordings were completed in an isometric strength testing chair.  Upon the conclusion of the four-week study, the results showed that MVF was significantly greater (P<0.001) within the MST group (21±12%) compared to the EST group (11±7%).  However, the early phase explosive force measured at 100-ms increased after the EST training protocol (16±14%), but not in the MST group.  The neuromuscular influences behind the MVF improvements of the MST group were reflected by two-fold greater changes in EMG-MVF than EST.  The more explosive improvements of the EST group were highlighted by the production of greater EMG-MVF in the early phase of neuromuscular activation during the explosive contractions⁴.

To develop a better understanding of the specificity of training in relation to RFD, Rhea and colleagues examined the influence of training at different squat depths on joint-angle specific strength along with a transfer to sports-related performance measures such as sprinting and jumping³.  The participants included 28-male collegiate athletes from various sports (Avg age=21.1-years) that were randomly assigned to a 16-week training protocol that included either the quarter squat (40-60⁰ knee angle), half squat (parallel 70 to 100⁰ knee angle), or the full squat (>100⁰ knee angle). Testing was conducted prior and after the training protocols; strength (1RM) testing was performed at all three depths, with the addition of the vertical jump and the 40-yard sprint test.  Upon conclusion of the 16-week training intervention, the results revealed that the athletes in the quarter and full squat protocols improved significantly more at those depths compared to the other two.  Although jump height and sprint speed improved in all groups, the quarter squat showed the greatest transfer to both performance measures (VJ=.15%/ES=0.75; Sprint=-0.02%/ES=0.58). The improvements observed by the quarter squat group and its joint-angle specificity has been associated to neurological control leading to greater degrees of neural drive when those angles were trained towards higher degrees of velocity resulting in adaptational responses³.

In conclusion, the specificity of training may be influenced by the degree to which maximal or explosive training is utilized in practice that effects RFD.  In addition, variations in joint-angles during training, specifically the quarter squat, may dictate a greater level of transfer when aiming to improve jump and sprinting abilities.  The increases in performance following these resistance training protocols become observable when performing the particular task used during training¹.  In addition, the understanding of the neuromuscular influences involved within each performance outcome may help guide strength and conditioning professionals during program design towards optimal performance within their sport.

References

1. Gardiner, PF, Advanced neuromuscular exercise physiology.  Champaign, IL: Human Kinetics, 2011.  

2. Haff, GG and NT Triplett, National Strength and Conditioning Association.  Essentials of strength training and conditioning (4^th ed.).  Champaign, IL: Human Kinetics, 2016.

    3. Rhea, MR, et. al., Joint-angle specific strength adaptations influence improvements in power in highly trained             athletes.  Human Movement, 17(1), 43-49, 2016.

4. Tillin, NA, and JP Folland, Maximal and explosive strength training elicit distinct neuromuscular adaptations, specific to the training stimulus.  European Journal of Applied Physiology, 114, 365-374, 2014. 

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Daniel Cobian, MS, CSCS, RSCC*D, CES is a Strength and Conditioning Coach for the Chicago White Sox.