International Journal of Sports Physiology and Performance, 2015, 10, 232-237 http://dx.doi.org/10.1123/ijspp.2014-0073 © 2015 Human Kinetics, Inc.
Assessment and Monitoring of Ballistic and Maximal Upper-Body Strength Qualities in Athletes Kieran P. Young, G. Gregory Haff, Robert U. Newton, Tim J. Gabbett, and Jeremy M. Sheppard Purpose: To evaluate whether the dynamic strength index (DSI: ballistic peak force/isometric peak force) could be effectively used to guide specific training interventions and detect training-induced changes in maximal and ballistic strength. Methods: Twenty-four elite male athletes were assessed in the isometric bench press and a 45% 1-repetition-maximum (1RM) ballistic bench throw using a force plate and linear position transducer. The DSI was calculated using the peak force values obtained during the ballistic bench throw and isometric bench press. Athletes were then allocated into 2 groups as matched pairs based on their DSI and strength in the 1RM bench press. Over the 5 wk of training, athletes performed either high-load (80–100% 1RM) bench press or moderate-load (40–55% 1RM) ballistic bench throws. Results: The DSI was sensitive to disparate training methods, with the bench-press group increasing isometric bench-press peak force (P = .035, 91% likely), and the ballistic-bench-throw group increasing bench-throw peak force to a greater extent (P ≤ .001, 83% likely). A significant increase (P ≤ .001, 93% likely) in the DSI was observed for both groups. Conclusions: The DSI can be used to guide specific training interventions and can detect training-induced changes in isometric bench-press and ballistic bench-throw peak force over periods as short as 5 wk. Keywords: bench press, isometric, bench throw, peak force, dynamic strength index The assessment and training of fundamental strength and power qualities have received extensive attention in the scientific literature. While there is still much debate on which tests and methods are most suitable for improving strength and power, there are several well-established principles that must be taken into consideration when attempting to improve performance in elite athletes. First, the ability to express high levels of upper-body maximal strength has been identified as an important performance quality in elite athletes.1 In addition, the potential long-term benefits of maximal strength training make it an ideal training modality to improve performance.2 Therefore, it is vital that any testing protocol and subsequent training intervention include a component of maximal strength. Second, the use of ballistic exercises such as the ballistic bench throw (BBT) is increasingly being assessed and implemented in sports that require high levels of upper-body strength and power.3,4 While the BBT is typically used to improve power output, further research is required to investigate the impact of maximal and ballistic strength training on force-producing capabilities of the upper body. Isometric assessments have been shown to be reliable when assessing upper-5 and lower-body6 force capabilities and are generally performed to quantify qualities of peak force (PF) and rate of force development. Unfortunately, there is little information available on the effects of upper-body maximal and ballistic strength training on isometric force production. While the comparison of isometric and isoinertial tests is not entirely novel,7 there is a paucity of data available investigating the use of these data in the Young is with the Canadian Sport Institute Pacific, Victoria, BC, Canada. Haff, Newton, and Sheppard are with the Centre for Exercise and Sports Science Research, Edith Cowan University, Perth, Australia. Gabbett is with the School of Exercise Science, Australian Catholic University, Brisbane, Australia. Address author correspondence to Kieran Young at kyoung@ csipacific.ca. 232
prescription of specific training interventions, with no known studies involving upper-body assessments. Detecting an athlete’s specific area of relative deficiency to improve performance is essential when attempting to maximize performance capacity. By focusing on the least developed component or performance “quality,” the greatest neuromuscular adaptation may be elicited due to the increased opportunity for adaptation resulting in superior performance improvements.8 One such method of detecting specific deficiencies in elite athletes is the assessment of the dynamic strength index (DSI). This ratio reflects the extent to which an athlete is able to apply force dynamically in relation to his or her maximal isometric force capabilities.9 It is expressed as a ratio of the ballistic PF to isometric PF: DSI = ballistic PF/isometric PF. Specifically, examination of the DSI suggests that athletes who are better able to translate their maximal force-generating capacities into explosive performances will have a higher ratio (ie, closer to a 1-to-1 ratio), while athletes who are not as efficient in using their maximal force-generating capacities will have a lower ratio. Thus, the DSI is indicative of the athlete’s force-generating potential into explosive movements. Generally, there are 2 ways to improve an athlete’s force output during explosive movements, including either increasing the athlete’s maximal force-generating capacity or decreasing the deficit between the maximal force-generating capacity and that achieved during the explosive activity.10 Theoretically, if an athlete has a high ratio for the DSI, including strength work designed to increase maximal force-generating capacity should result in improved performance.10,11 Conversely, if the athlete has a low ratio, he or she may benefit from training that focuses on the development of force generation during explosive activities.10 While this is conceptually sound, there is a paucity of research directly examining the DSI and its use in guiding training practices. Sheppard et al9 used PF obtained from a squat jump and PF during an isometric midthigh pull to calculate a DSI. In that study a DSI of 0.80, targeting maximal force-development capacities was suggested to elicit the greatest neuromuscular adaptation. Similarly, Wilson and Murphy8 used a ratio of rate of force development to PF in the isometric squat to calculate a DSI. They concluded that recreational athletes would benefit most from an increased emphasis on maximal strength training to improve cycling performance if the ratio was >3.1. Conversely, if the ratio was
Assessment and Monitoring of Ballistic and Maximal Upper-Body Strength Qualities in Athletes Kieran P. Young, G. Gregory Haff, Robert U. Newton, Tim J. Gabbett, and Jeremy M. Sheppard Purpose: To evaluate whether the dynamic strength index (DSI: ballistic peak force/isometric peak force) could be effectively used to guide specific training interventions and detect training-induced changes in maximal and ballistic strength. Methods: Twenty-four elite male athletes were assessed in the isometric bench press and a 45% 1-repetition-maximum (1RM) ballistic bench throw using a force plate and linear position transducer. The DSI was calculated using the peak force values obtained during the ballistic bench throw and isometric bench press. Athletes were then allocated into 2 groups as matched pairs based on their DSI and strength in the 1RM bench press. Over the 5 wk of training, athletes performed either high-load (80–100% 1RM) bench press or moderate-load (40–55% 1RM) ballistic bench throws. Results: The DSI was sensitive to disparate training methods, with the bench-press group increasing isometric bench-press peak force (P = .035, 91% likely), and the ballistic-bench-throw group increasing bench-throw peak force to a greater extent (P ≤ .001, 83% likely). A significant increase (P ≤ .001, 93% likely) in the DSI was observed for both groups. Conclusions: The DSI can be used to guide specific training interventions and can detect training-induced changes in isometric bench-press and ballistic bench-throw peak force over periods as short as 5 wk. Keywords: bench press, isometric, bench throw, peak force, dynamic strength index The assessment and training of fundamental strength and power qualities have received extensive attention in the scientific literature. While there is still much debate on which tests and methods are most suitable for improving strength and power, there are several well-established principles that must be taken into consideration when attempting to improve performance in elite athletes. First, the ability to express high levels of upper-body maximal strength has been identified as an important performance quality in elite athletes.1 In addition, the potential long-term benefits of maximal strength training make it an ideal training modality to improve performance.2 Therefore, it is vital that any testing protocol and subsequent training intervention include a component of maximal strength. Second, the use of ballistic exercises such as the ballistic bench throw (BBT) is increasingly being assessed and implemented in sports that require high levels of upper-body strength and power.3,4 While the BBT is typically used to improve power output, further research is required to investigate the impact of maximal and ballistic strength training on force-producing capabilities of the upper body. Isometric assessments have been shown to be reliable when assessing upper-5 and lower-body6 force capabilities and are generally performed to quantify qualities of peak force (PF) and rate of force development. Unfortunately, there is little information available on the effects of upper-body maximal and ballistic strength training on isometric force production. While the comparison of isometric and isoinertial tests is not entirely novel,7 there is a paucity of data available investigating the use of these data in the Young is with the Canadian Sport Institute Pacific, Victoria, BC, Canada. Haff, Newton, and Sheppard are with the Centre for Exercise and Sports Science Research, Edith Cowan University, Perth, Australia. Gabbett is with the School of Exercise Science, Australian Catholic University, Brisbane, Australia. Address author correspondence to Kieran Young at kyoung@ csipacific.ca. 232
prescription of specific training interventions, with no known studies involving upper-body assessments. Detecting an athlete’s specific area of relative deficiency to improve performance is essential when attempting to maximize performance capacity. By focusing on the least developed component or performance “quality,” the greatest neuromuscular adaptation may be elicited due to the increased opportunity for adaptation resulting in superior performance improvements.8 One such method of detecting specific deficiencies in elite athletes is the assessment of the dynamic strength index (DSI). This ratio reflects the extent to which an athlete is able to apply force dynamically in relation to his or her maximal isometric force capabilities.9 It is expressed as a ratio of the ballistic PF to isometric PF: DSI = ballistic PF/isometric PF. Specifically, examination of the DSI suggests that athletes who are better able to translate their maximal force-generating capacities into explosive performances will have a higher ratio (ie, closer to a 1-to-1 ratio), while athletes who are not as efficient in using their maximal force-generating capacities will have a lower ratio. Thus, the DSI is indicative of the athlete’s force-generating potential into explosive movements. Generally, there are 2 ways to improve an athlete’s force output during explosive movements, including either increasing the athlete’s maximal force-generating capacity or decreasing the deficit between the maximal force-generating capacity and that achieved during the explosive activity.10 Theoretically, if an athlete has a high ratio for the DSI, including strength work designed to increase maximal force-generating capacity should result in improved performance.10,11 Conversely, if the athlete has a low ratio, he or she may benefit from training that focuses on the development of force generation during explosive activities.10 While this is conceptually sound, there is a paucity of research directly examining the DSI and its use in guiding training practices. Sheppard et al9 used PF obtained from a squat jump and PF during an isometric midthigh pull to calculate a DSI. In that study a DSI of 0.80, targeting maximal force-development capacities was suggested to elicit the greatest neuromuscular adaptation. Similarly, Wilson and Murphy8 used a ratio of rate of force development to PF in the isometric squat to calculate a DSI. They concluded that recreational athletes would benefit most from an increased emphasis on maximal strength training to improve cycling performance if the ratio was >3.1. Conversely, if the ratio was
