Average performance times, SL, SF, and joint angles were calculated across the 3 trials for SA and CODA. Performance times are presented as means and SD. Coefficient of determination (r2) and independent t-tests were used to compare the faster and slower groups on the variables of interest. Statistical significance was set at p ≤ 0.05.
The squad rankings for SA and CODA tasks based on 2.5-m times can be observed in Table 1. Those players with faster 2.5-m times in the SA task did not necessarily perform equally fast in the CODA task (r2 = 0.15). Five of the 22 players dropped from the faster group in the SA task to the slower group in the CODA task, and conversely, 5 players also improved from slower in the SA task to faster in the CODA task.
In terms of the group comparisons, only 1 variable differed significantly between groups for the CODA task. Significantly higher average SF (4%, p = 0.03) was observed for the faster group when compared with the slower group (Table 2).
For the SA task, faster times were associated with significantly smaller average SLs (7%, p = 0.03), greater torso angles (i.e., greater forward lean; 30–37%, p < 0.001), and smaller hip angles (less knee lift) in the first step (21–22%, p = 0.00). On average, the faster group had smaller SLs, higher average SF, and a lower knee lift than the slower group.
With regard to the task comparison, the SA task was associated with significantly longer average SLs (21–23%, p = 0.00; Table 2) and significantly longer SL across all 3 steps than the CODA task (17–27%, p < 0.001; Table 3). Additionally, a significantly larger torso angle was associated with the first step of the SA task (34%, p < 0.001) and significantly smaller hip angles for the first and second steps of the SA task (11–22%, p = 0.00 and 0.04, respectively).
Acceleration in court-based team sports such as netball and basketball is typically confined to a relatively small area, which is defined by boundary lines or opponents. As such, players are often not able to accelerate for >2.5–5 m before an evasive COD is required (22,24). However, the majority of research addressing acceleration technique is from a static start over >5 m (i.e., more reflective of track sprinting ability as opposed to game speed ability) (5,6,10,13–15,18,26). As the objectives of acceleration movements performed across sports vary considerably and the relationship between SA and CODA is typically quite poor (24), it is likely that SA technique also differs considerably from that of the more sport-specific CODA technique. Consequently, the primary purpose of this article was to compare the stride characteristics and body positioning adopted by faster and slower court-based team players during the first 3 strides when accelerating in an SA with those of the acceleration after a rapid 180° ground-based COD movement (i.e., CODA).
When the kinematics (i.e., SL, and hip and torso angles) of each group was compared, several differences were observed between the SA and CODA tasks. Unlike Mann and Herman's (18) findings that reported 3% longer SLs in faster straight sprinting performances, abbreviated (7–8%) average SL and individual SLs were observed in the faster SA performances in the present study. Although average SF was not significantly different between groups for the SA task (p = 0.13), it was approaching significance and it may be speculated that the higher SF of the faster group was that which differentiated the 2 groups (i.e., because velocity = SL × SF). In terms of increasing player first step quickness, it would seem that cuing faster SF or conversely teaching players not to overstride may optimize 2.5-m sprint performance.
Although average SFs observed in this study were greater than those reported in previous research (4.01–4.45 Hz (14,18)), the sample of participants and data collection varied greatly to those of the present study. The participants of the current study were female court-based sport players, whereas previous research was conducted using Olympic-level male sprinters (18) and male athletes from various field sports (14). It has been documented that track speed is different to field sport speed (7,8,16,25), with most players achieving maximum velocity in a shorter distance compared with track athletes. As such, it is likely that those athletes that need to accelerate quicker over shorter distances would have different step kinematics (i.e., SF). Additionally, in both of these previous studies, the SFs were calculated during a midsection of a sprint >10 m from the start of the task (to the knowledge of the authors of the current study, no research has investigated acceleration kinematics over 2.5–5 m), whereas the present study reported SFs over the first 3 steps from a static start. These 2 factors likely contributed to the difference in reported SFs.
The faster players also had a higher knee lift (decreased hip angle) and increased torso angle (increased forward lean) in the SA task. A higher knee lift at takeoff would increase the time the free leg is spent in the air, thereby allowing for a larger SL to be attained through each step. However, this was not the case for the faster athletes, and in fact, their SL was significantly less than that of the slower players. It can only be speculated that even though there was higher knee lift, the velocity of limb movement was quicker in the fast group (e.g., SF), the product being a leg that drives down into the ground further, faster, and more rearward. It is likely that greater propulsive ground reaction forces result; however, further analysis (e.g., force plate) would be needed to investigate this contention.
During the acceleration phase of straight-line sprinting, a forward lean of the torso of up to 45° has been reported as being “optimal” (3,5,9) in elite-level sprinters. The SA torso angle in the current study (32.3–39.3°) was similar to that reported in a previous research by Atwater (3) (15–45°) over the first 3 steps of an SA performance in elite sprinters. An increased forward lean (increased torso angle) at takeoff in the SA task assists in the ability to accelerate as the body's center of mass is brought ahead of the base of support. This allows for increased horizontal propulsive forces to be applied into the ground (26) at takeoff.
In terms of the task comparisons, when performing the SA task, all players had longer SLs, increased torso angle for the first step, and decreased hip angles for the first 2 steps than observed for the CODA task. When a player is accelerating after a rapid COD, the free leg must first rotate around into the new direction before driving upward. In contrast, during the SA task, the knee can be driven upward immediately after takeoff. As a result, a higher knee lift (as observed in the SA task) allows more time for the lower leg to extend into a longer SL. The longer the free leg is airborne through the swing phase, the longer it will take before a horizontal or lateral force can be applied into the ground for a COD movement. The increased forward lean associated with the SA task allows for increased stability and horizontal-vertical propulsive forces into the ground at takeoff (26). Therefore, the more erect posture associated with the CODA task (i.e., an abbreviated SL, decreased forward lean, and decreased knee lift) will be more advantageous when performing consecutive COD movements because the free leg is able to be repositioned earlier for the next ground contact.
Consistent with previous research (24), players who performed well in one task did not necessarily perform equally well in the other task (as observed by the low shared variance of performance times and task). This finding is reinforced by the data in Table 1 where quite substantial differences in rankings between the SA and CODA tasks can be observed for some players. The value of such an analysis is in the ability to diagnose athletes who have SA or COD limitations. Identifying either as a problem will thereafter involve very different strategies by the coach and strength and conditioning practitioner to remediate the limitations. That is, an athlete who has a faster sprint time but a slower CODA time would most likely benefit from technique training around changing directions. Conversely, athlete with a slower sprint time would most likely benefit from explosive strength and power type training. With regard to the first scenario, where the CODA time is slower, identifying those technical cues that are predictors of faster performance would seem of practical value. For this to occur, a sport-specific approach using a relevant CODA task would seem prerequisite to identifying those factors that optimize sport-specific COD performance. An assessment tool that more closely resembles the movement characteristics required in competition increases both the validity of the assessment itself and the diagnostic value to the strength and conditioning coach.
This study has not exhaustively investigated the technical characteristics specific to SA and CODA tasks. Insights into the differences in the technical characteristics when performing 2 forms of acceleration tasks for faster and slower players have been identified based off of kinematic data. Those qualities consistently present in faster performances (e.g., more erect posture at takeoff and decreased SL and knee drive for CODA when compared with SA performances) would seem desirable qualities to emphasize in training sessions for all levels of players. Additional research is needed to further examine the technical qualities that contribute to faster sport-specific acceleration performances.
It should be noted that one limitation of this study was that the trials were not randomized. Although the effects of fatigue are likely not an issue with the tasks in this study, it is possible that learning effects may be present. If further research is conducted following the procedures outlined in this study, this learning effect should be taken into account and a randomized trial order is recommended.
The faster players observed in this study had several kinematic differences between SA and CODA tasks when compared with the slower players. Because these characteristics are associated with more optimal force productions and resulting velocities through the acceleration phase of sprinting, emphasizing those technical characteristics that were associated with the faster players' SA (decreased SL, increased forward lean and knee lift in the initial step) and CODA (increased SF) performances in the training programs of all players would likely improve SA and CODA performances, respectively.
The results from this study also indicate that the technical characteristics of SA are not the same for CODA. The goal of SA is to attain maximum velocity as quickly as possible. In contrast, CODA requires players to accelerate as quickly as possible after a rapid directional change and may also occur before a subsequent COD movement. As a result, the body positioning and posture differ greatly between the 2 acceleration tasks (i.e., a more erect posture at takeoff and decreased SL and knee drive for CODA when compared with SA performances). Task-specific training programs that target these features may lead to improved performance times in each respective task and possibly increase transference into the sport.
When group means are compared, a great deal of information regarding individual player strengths and weaknesses is lost. Investigating the intersquad player rankings in various tasks (i.e., SA vs. CODA) can give insights into the task-specific capabilities of players and areas in need of improvement within the movement sequence. Likewise, when raw kinematic values of players are compared, individual technical weaknesses may be identified. As a result, programming can be guided to a better effect. Although this study investigated only 4 kinematic features of SA and CODA performances, additional research that examines these characteristics and additional kinematic variables (e.g., knee angle at touchdown) over a variety of movement tasks that are commonly performed in sport will further increase our understanding of training and programming for acceleration in sport.
We thank the New Zealand national under-21 training squad and coaches for participating in this study. This study was supported by Netball New Zealand and Auckland University of Technology's Sports Performance Research Institute New Zealand who cofunded the academic scholarship of the primary researcher.
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Keywords:© 2013 National Strength and Conditioning Association
step length; step frequency; knee lift; sprinting; technique