Speed is often considered an essential element to athletic success. In general terms, most would agree that a faster athlete has a distinct competitive advantage over their slower competition. For this reason, athletes tend to spend a great deal of time engaged in activities to improve running velocity. However, the strength and conditioning professional must consider that outside of track and field events, speed in most team-based sports, such as soccer, football, and hockey, is characterized by abrupt changes in velocity and requires a variety of adjustments in foot placement, stride rate, and stride frequency to be effective (4,34). Based on these demands, the athlete must be able to generate explosive muscular forces very rapidly to accelerate, change directions, and then re-accelerate over relatively short distances (approximately 10–30 m) (3,5,9). Therefore, to be successful, acceleration rather than maximal velocity is likely a greater predictor of success in these types of sports. For this reason, it would appear that the aim of training for these athletes should be on the ability to change velocity over short distances in multiple directions based on game-specific stimuli rather than dedicating the majority of their training time to developing linear speed alone (12,13,34).
Acceleration can be defined as the rate at which a person or object changes velocity (29). Expressed in mathematical terms, it is the change of velocity divided by the change in time (a = v/t). Most sport coaches view acceleration as the athlete’s ability to produce high speeds within 5–10 m from a stationary or moving start (10). It has been reported that some athletes are able to achieve peak rates of acceleration within the first 8–10 strides from a stationary start, allowing them to reach up to 75% of their maximum running velocity within the first 10 yards (18). This ability to explosively accelerate is largely dependent on the athlete’s ability to overcome inertia (17). Inertia is the tendency of an object to resist change in motion and relates to Newton’s first law of motion, which states that every object continues in its state of rest or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it. Therefore, to produce movement, an athlete must apply greater muscular forces into the ground to overcome the oppositional forces of gravity to produce velocity (17). It is most difficult to overcome inertia from a stationary start, as the body is at rest. Duthie et al. (9) found that elite rugby union players were able to achieve 70% of their maximum velocity within 2 seconds from a standing start. In comparison, when observing Australian Rules football players, Benton (3) discovered that these athletes were able to achieve greater acceleration speeds and near maximal velocities (96–99% of mean maximal velocity) when sprint efforts commenced from a moving (i.e., jogging or striding) rather than a stationary start. Duthie et al. (9) also found the initial velocity of rugby union players was significantly better when performing a sprint from a walking, jogging, or striding start compared with a standing start.
Although many would argue that maximal velocity training is not important for the field/court sport athlete, at times these athletes may be required to achieve near maximal velocities when accelerating from a rolling or striding start. Thus, performing some maximal velocity training within an athlete’s training session is warranted. However, the amount of time spent training this element should be based on a game’s needs analysis. For example, Benton (3) observed that Australian Rules football players frequently (65–85%) started sprint efforts from a moving start (i.e., jogging or striding) rather than a stationary start. For these reasons, it would seem prudent that speed training sessions would emphasize acceleration from different types of both stationary and moving starts based on these percentages. In addition, incorporating some maximal velocity training drills that require rapid acceleration from a rolling or moving start may be more sport specific than always performing these drills from a traditional stationary start.
METHODS OF IMPROVING ACCELERATION
There are 3 primary areas that can be trained that will directly improve an athlete’s ability to accelerate (17). These domains include the following:
- Increasing the number of steps (increasing stride rate) without decreasing the length of each stride.
- Increasing the length of each stride without decreasing stride rate.
- Improving sprinting technique that will result in less wasted energy and greater force production and utilization.
Most training methods associated with increasing stride frequency emphasize improving leg turnover, such as using overspeed training methods like running downhill or towing. In contrast, training methods aimed at improving stride length tend to focus on training the athlete to increase their force output at foot strike rather than attempting to increase limb velocity. Because this article is specifically focused on developing power to improve acceleration, methods aimed at improving stride length, rather than stride frequency, will be addressed.
POWER AND ACCELERATION
There are a variety of methods that can be used to improve acceleration through improved stride length. Typically, these training methods focus on strategies that help the athlete exert a greater amount of force into the ground at foot strike. According to O’Shea (25), one of the major benefits of being a powerful athlete is the ability to accelerate faster than an athlete who just possesses great strength. Therefore, the ability to generate explosive force is critical for acceleration. However, though ground contact time during acceleration is slightly longer in comparison with maximal velocity sprinting, it is not possible to generate maximal force at foot strike during any phase of the sprinting cycle (23,33). Therefore, it is not just the amount of force the athlete is able to exert but how quickly they are able to produce this force. Accordingly, when we look at power in the context of game speed, rate of force development (RFD) and peak force production are likely of greater significance than maximal force development during these activities (35,36). Because power is the expression of both strength (force) and speed (velocity), it is generally accepted that improving force production potential, velocity of movement, or both are effective when seeking to improve acceleration (28). Although maximal force and velocity exist on the 2 extreme sides of the power continuum (7) (Figure 1), training both maximal force production and RFD may directly influence an athlete’s ability to express the appropriate amount of power to execute a given task during competition.
Many coaches use resistance training as a method of improving force production capabilities and then transition this newly acquired strength to exercises/drills that emphasize the actual speeds in which these forces are expressed during competition (4). Hence, the emphasis of heavy resistance/low-velocity strength training is to influence the high-force end of the force-velocity continuum (35). According to Cavanaugh (7), the rationale for this approach is to improve strength so that the force required to move a given resistance, such as bodyweight, would represent a smaller percentage of the athletes increasing level of maximal strength. The ability to generate greater ground reaction forces (GRF) at foot strike should allow for greater stride lengths to be achieved, thus improving the speed at which one is able to accelerate.
This concept directly relates to Newton’s third law of motion, or the law of action-reaction. When an athlete pushes the foot back and downward, the mutual interactions between the foot and ground will act to propel the athlete forward. The amount of force exerted by the athlete is equal to the amount of force on the athlete. As a result, the direction of the force on the ground (backward) is in direct opposition to the direction of force on the athlete (forward). Based on this interaction, it would seem prudent to train the muscles of the lower extremity directly responsible for generating forces at foot strike, specifically those muscles surrounding the hip.
During the propulsion phase of acceleration, the hip extensors and quadriceps muscles are directly responsible for generating explosive forces (37). The hamstring muscles also play a major role in decelerating the lower leg in preparation for ground contact, in addition to aiding in hip extension (33,37). Training the muscles of the hip flexors is also imperative because greater strength and power in these muscles is essential for accelerating the hip forward from an extended to flexed position to reload the hip for subsequent ground contact (33).
In general, multijoint closed kinetic chain exercises such as various types of squats as well as multidirectional lunges (Figure 2) and step-ups (Figure 3) would be preferred over the utilization of resistance training machines based on their biomechanical similarities to actual running events. In addition, these free weight type exercises require the athletes to stabilize, control, and resist unwanted movements during their performance. This may potentially aid in greater joint stability as energy is transferred from the ground up through the kinetic chain, which may improve horizontal displacement (26). However, exercises targeted at improving the eccentric strength of the hamstring muscles, such as traditional and single leg variations of the Romanian deadlift (Figures 4 and 5), multiplanar reaching lunges (Figure 6), glute-ham raises (Figure 7), and traditional and assisted versions of the Nordic leg Curl (Figures 8 and 9), may also be beneficial in terms of improving force production and reducing injury risk (2,6).
Another form of resistance training to improve acceleration is the use of resisted sprinting. Resisted sprinting requires the athlete to perform sprint training with weighted sleds or vests, parachutes, tires attached to harnesses, partner-resisted drills, and uphill/stair running (8,22). The main objective of this form of training is to increase force production through improvements in stride length. Although sleds and resisted methods have been shown to improve acceleration speed up to about 10 m, the weight used should not exceed 10–12.6% of the athletes total body mass (BM) to minimize the disruptions of proper sprint kinematics (16,20,22,32). Although Lockie et al. (20) found that heavier sled work (32.2% of total BM) did increase upper-body involvement, it also caused reductions in step length and stride rate, and increased ground contact time. Furthermore, it has been recommended that the amount of load added to these types of training devices should not result in a greater than 10% drop off in an athlete’s speed limit (15). Several authors have reported that a training load of up to 10% BM fell within these limits (20,22).
IMPROVE STRENGTH TO BODYWEIGHT RATIO
Because acceleration is a product of force/mass, to improve acceleration, we must either increase the amount of force produced or decrease the amount of mass the athlete is required to move. Quite often in an attempt to increase force production capabilities, athletes seek to increase their BM. Because the muscle is active and produces force, those individuals with greater muscle cross-sectional area are typically able to produce greater forces. However, when we increase the mass, the body has to overcome a greater amount of inertia to move (F = M × A). This concept is illustrated by Newton’s second law of motion, which states that there is an inverse relationship between mass and acceleration. For instance, Lockie et al. (19) found that although no absolute strength differences existed in the 3 repetition maximum squat for 2 groups of athletes, it was discovered that the faster group of athletes displayed greater relative strength in comparison with their BM. Although greater force may be produced, if the athletes weight also increases, additional force is required to move this mass. Therefore, in some cases, attempting to increase the muscle mass to improve speed and acceleration yields a zero sum gain or even slower acceleration times.
Another method of improving the strength to bodyweight ratio would be to decrease an individual’s amount or percentage of body fat. Intuitively, it makes sense that reducing one’s nonfunctional mass (body fat) may be a more productive approach to improving speed and acceleration than first attempting to add mass because less force is required to overcome inertial forces. This allows the athlete to fully maximize their current force production potential without adding additional mass. Conducting initial body composition estimations may be beneficial to the athlete, coach, and nutritional professional because it aids in the development of appropriate training and nutritional interventions to achieve ideal body compositions to maximize performance.
Power can be expressed as force × velocity. As previously stated, although the ability to produce force is important to acceleration, this force must be applied rapidly to maximize performance. Research indicates that there is a significant relationship between both lower-body power and acceleration (14,21,30,31). For this reason, various forms of power training, such as weightlifting and plyometrics, are frequently used to help bridge the gap between strength and power (1,35) Research has shown that these 2 forms of exercise have a significant correlation to sprint speed and acceleration (14,30,31).
Weightlifting refers to the competitive sport of lifting barbells as practiced in the Olympic Games. The 2 lifts in weightlifting are the snatch and the clean and jerk. These exercises necessitate exerting high forces against the ground in a very rapid manner. Thus, these lifts may have a greater dynamic correspondence to acceleration compared with traditional slow speed resistance training (14,24). The hang power clean refers to starting with the barbell off of the ground (normally just above the knees) and then “catching” it at shoulder height. The hang power clean is relatively easy to learn compared with the power clean from the floor, and athletes are able to generate high power outputs when performing this exercise. As a result, the hang power clean is a staple exercise for many strength and conditioning coaches who use weightlifting movements in their training (24). Other exercises that may be used as alternatives to weightlifting would include barbell or dumbbell speed and jump squats (Figures 10 and 11).
Plyometrics are training drills that rely heavily on the stretch shortening cycle (SSC) and the conversion of the eccentric loading to concentric force production (11). By enhancing the ability of the muscle tendon unit to produce force rapidly, an athlete has a significant opportunity to improve their levels of reactive strength (11,31). Because plyometric drills range in intensity from low loads (e.g., pogos) to moderate loads (e.g., squat jumps) to high-intensity shock drills (e.g., depth jumps), this form of training would allow the athlete to target a wide spectrum of the power continuum. In addition, performing plyometrics would be considered a very specific method of training to improve acceleration during running because of the similarity in load (bodyweight), demands on the SSC, and the RFD required for these drills (7)
It has been suggested that although both horizontal and vertical production of force is important to athletic performance, it is the horizontal forces that experience the greatest increases when accelerating to maximal velocity (28). Therefore, it would seem prudent to incorporate both vertical and horizontal plyometric drills into the athlete’s training program to enhance horizontal power production. However, plyometric drills that emphasize horizontal, rather than vertical, force production appear to be more specific to the running motion and should be emphasized if horizontal power is the primary training goal. Currently, there are no recommendations available that provide the ideal ratio of vertical to horizontal training drills that should be performed. Thus, at the moment, this is largely based on practical experience and the coaches’ best judgment. Hence, the strength and conditioning coach should evaluate how much time and emphasis is placed on performing vertical power training exercises in comparison with horizontal training drills and seek to determine the optimal balance between force production in these 2 directions.
An important consideration for the strength coach to consider when incorporating bounding type drills into an athlete training program is ensuring they have an adequate base of strength to accommodate the stress placed on the joints upon landing. It has been suggested that an athlete be able to perform back squats with at least 1.5× bodyweight before attempting high-level plyometric drills (27), especially those that require a single leg landing. However, various hopping and skipping drills may be used by athletes to train this horizontal component predicated on their ability to maintain proper form and maintain good body control throughout the required ranges of motion to perform these drills.
Finally, when seeking to improve an athlete’s ability to explosively accelerate, the importance of proper technique cannot be overstated. Those athletes who are able to harness their force and power by positioning the joints in the most efficacious biomechanical positions to exert high forces into the ground more efficiently have a distinct competitive advantage. Good form and technique allow the athletes to work more efficiently in not only improving acceleration speed, but also allowing them to conserve energy and resist fatigue.
The mechanics of acceleration differ from those of maximum velocity, and in the authors’ opinions, the majority of time spent coaching nontrack athletes on “speed development” should be devoted to this phase. Generally, it is agreed by most experts that speed can be improved with proper training. However, it should be mentioned that to achieve excellence in any domain, athletes have to spend a considerable amount of time to improve performance through practice-related activities. The acquisition of proper sprinting mechanics to improve accelerative capabilities is no exception. Regardless of the athlete’s starting stances, the primary emphasis is to drive down into the court or field and build momentum. In using a top to bottom approach, the practitioners will have systematic approach and several key reference points they can refer to when coaching their respective athletes.
A good place to begin is with the athlete’s posture, which refers to the alignment of the body. During acceleration, the athlete’s body will have a pronounced forward lean that results in a lower center of mass position. This forward lean also allows optimal body positioning for the production of greater forces to increase horizontal propulsion. It is critical that this lean not be achieved by flexing or bending at the waist. It should be noted that during all phases of sprinting, one should be able to draw a straight line from the head, through the torso, hip, knee, and ankle of the supporting leg when the athlete’s leg is fully extended just before the foot loses contact with the ground.
Next, the head position should be addressed. The head should be in line with the torso and the torso in line with the legs during linear acceleration movements. Excessive flexion or extension of the neck is not warranted, and the athletes should be coached to avoid swaying or jerking of the head in any direction.
Proper arm action is critical to maximizing one’s acceleration potential. Arm action refers to the range of motion and velocity of the athlete’s arms. The athlete should be instructed to initiate his/her aggressive arm swing at the shoulder with the elbow flexed to approximately 90°. The movement of the arms counteracts the substantial rotational forces being generated by the legs. Additionally, the forceful backward swinging of the arms will use the stretch reflex and provide much of the forward propulsion of the contralateral arm.
Finally, proper leg action should be examined. In this context, leg action deals with the relationship of the hips and legs relative to the torso and the ground. Manufacturing explosive take-offs requires extending the hip, knee, and ankle in a synchronizing manner to elicit the most efficient force against the ground. In coaching acceleration form drills, athletes should be instructed to keep their feet in a dorsiflexed position throughout the running cycle, except when the foot strikes the ground. During foot strike, the weight should be on the ball of the foot, directly under the athlete. This action will minimize braking forces and maximize propulsive force. The angle of the athlete’s shins to the ground will be sharp (less than 90°) initially, but it will increase slightly with each successive stride. During acceleration, stride length starts out short and increases gradually. Ground contact time will be the greatest with the first stride, and then it also gradually decreases with stride progression. Similarly, stride frequency will start out slowly because of the initial longer ground contact times, and it will increase gradually with each stride.
The need for explosive power during acceleration is evident in most team sports. The following are several considerations that should be considered when developing training programs to improve acceleration.
- Strength and conditioning professionals should conduct a basic game needs analysis to determine the average number of sprints and the range of these distances during competition. The number of times these sprints are initiated from a moving and stationary start should also be examined. In addition, the stances used for these stationary starts (3-point, 2-point, staggered, etc) should be examined to improve sport specificity when designing acceleration drills.
- Both vertical and horizontal power training exercises and drills should be performed to improve acceleration. These drills may better improve the athlete’s ability to use the reactive and neural benefits of the SSC during acceleration. However, because running is predominately performed horizontally, plyometric training drills aimed at horizontal force production may be more specific to these actions.
- Strength training should be performed to improve both absolute and relative strength levels to maximize the ability to produce, reduce, and stabilize forces during linear acceleration or accelerating with multiple changes of direction. Particular emphasis should be placed on lower-body exercises that require multijoint, closed kinetic chain free-weight exercises in multiple planes of movement and use the entire muscle contraction spectrum (concentric, isometric, and eccentric). The hip extensors should be trained to aid in the production of force at foot strike and generate greater horizontal propulsive forces. The hip flexor muscles should be trained to help improve stride frequency by allowing the athlete to reposition the leg quicker after foot strike to load the leg for subsequent hip extension and propulsion. Training the hamstrings using exercises that emphasize dynamic eccentric control may not only be useful for improving performance but also reducing injury risk.
- Although resisted sprinting may be a viable method of improving acceleration speed, this form of training should be used only after athletes have demonstrated a solid technical base. The training load used for resisted sprints should be at approximately 10–12% of the athlete’s total BM to effectively overload these movements without creating significant reductions in top speeds (<10%) to maximize adaptations and minimize disruptions in running form and technique.
- Although improving absolute strength may have a positive influence on the amount of GRF produced at foot strike, aiming to improve relative strength may have a greater impact on performance. Athletes should first strive to attain ideal body composition ratios based on the specific demands of their sport before trying to significantly increase muscle mass because greater force is required to move the additional load and may inevitably have no impact or even reduce one’s velocity.
- A wide variety of techniques should be used to improve both ends of the power continuum. Traditional resistance training should be performed to improve maximal force production potential. Weightlifting, and/or other forms of ballistic weight training, and plyometrics should be used to target more global parts of the power continuum, whereas high-speed/velocity activities, such as sprinting and agility training, should be used to address the expression of power in a game-specific context.
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Keywords:© 2012 by the National Strength & Conditioning Association
acceleration; game-speed; change of direction speed; power development