The relationship between strength, power and ballistic performance

Abstract

The purpose of this investigation was to answer the question, “Does Stronger Mean Faster?”. After a screening for elbow strength and speed, four groups of 8 subjects were selected for further investigation that fell into the extreme quartiles of the strength and speed continuums. The main investigation employed an apparatus that could freely rotate in the sagittal plane. Three isometric trials were performed at 60°, 90° and 120° of elbow extension. Dynamic trials were performed with relative resistances (0, 20, 40, 60 and 80%), determined from the lowest maximum isometric torque produced from the three joint angles mentioned above, and absolute resistances of 1.1 kg and 2.2 kg. A 1:1 relationship between strength and speed was not established (r = 0.498). Normalized peak power proved to be the best kinetic variable for predicting peak velocity (r ranging between 0.793 and 0.918). Individuals with similar peak torques were compared and the patterns of torque development, whether torques peaked early or late during the movement, physiologically agreed with known theoretically established mechanical responses. Similar velocities were also achieved with different peak torques demonstrating a timing issue. Estimated fibre-typing could not account for the performance differences.

Introduction

Many human movements are of a ballistic nature. Some individuals are capable of performing these fast movements much more rapidly than others. What makes one person capable of achieving a greater final velocity is the focus of this paper. To achieve a greater final velocity, an individual would have to develop more force, over a given distance, than another individual. Hochmuth and Marhold (1977) remind us that most human movements are constrained to a distance over which forces can be developed.

Since most human movements require time to build up to peak force, how does the pattern of force development influence the movement outcome? Dowling (1992) has shown that even in situations where the movement is constrained to a given distance (range of motion) and time is required to build up to peak force, the force pattern (see Fig. 1a) greatly affects the final velocity (see Fig. 1b) and movement time (see Fig. 1c) even if the peak force is not altered. A movement in which the peak force occurs early on is characteristic of a short movement time whereas a movement that achieves the same peak force later in the movement demonstrates a higher final velocity.

When analyzing the power between the two different movements, it was noted that the force pattern whose peak occurred later in the movement required a greater peak instantaneous power and required that it occur later in the movement as well (see Fig. 1d). Therefore, even if the same peak force is achieved, the pattern of force development will determine whether a movement will be one of short duration or one with a higher final velocity.

This notion of developing large amounts of peak power, particularly near the end of a movement, seems to be critical in the successful execution of a ballistic task. For vertical jumping, Dowling and Vamos (1993) analyzed 19 temporal and kinetic variables from the force-time and power-time curves to determine which characteristics were reflective of a good performance. From the ninety-seven young adults examined in this study, peak positive power was found to be the single best predictor of a good performance. The analyses performed on the vertical jumping data, however, did not tease apart the effects of countermovement (Asmussen and Bonde-Petersen, 1974, Bosco et al., 1982, Chapman and Sanderson, 1990, Dowling, 1992, Kawakami et al., 2002, Van Ingen Schenau, 1984), arm-swing (Feltner et al., 1999, Harman et al., 1990, Wrbaskic et al., 2002) and coordination (Tomioka et al., 2001) which can individually, or in combination, improve performance and be the difference between a good and poor outcome.

When training is concerned, Kaneko et al. (1983) demonstrated that maximal effort training at 0% load was the best stimulus for the improvement of maximum velocity at that load while 100% training of maximum load improved strength the most. They concluded that modifications to the force-velocity curve could be achieved and that the most effective stimulus for improving maximum power output should be at 30% of maximum strength. Therefore, stronger is not faster.

Wilson et al. (1993) echoed that response by showing that explosive weight training that maximized power output improved vertical jump height the greatest. The next best training response was observed by a plyometric training group which was followed by a weight-training group. Caiozzo et al. (1981) demonstrated that high velocity training only improved the torques at high velocity but that low velocity training increased the torques at both low and high velocity. Therefore, stronger is faster.

A control group was capable of achieving the similar elbow extension velocities as that of karate-trained individuals at preloads of 0 and 10% of their respective maximum voluntary contractions (Zehr et al., 1997). It was noted that the karate group displayed evidence for a superior performance in a velocity/load specific response. Therefore, stronger is faster.

The purpose of this investigation was to determine the relationship between strength and speed without any other confounding factors such as the coordination of multi-segments, transfer of momentum between body segments and countermovement enhancement. Therefore, the single-joint movement of elbow extension was chosen to be analyzed. The triceps muscle is the main muscle for achieving elbow extension, thus, a ‘one-muscle-to-movement outcome’ scenario can be discussed. This situation is not observed at other joints where force-sharing would most likely occur during movements.