The purpose of this study was to examine the acute effects of various types of stretching conditions of the IP muscle on 40‐yard sprint times in recreational runners. The authors found that the SS condition did not adversely affect performance nor were there significant changes in pre‐post sprint times in the BS or DS conditions. However, a significant improvement in time from pre‐ to post‐condition was observed in the NS condition. As such, the present study supports other studies found in the literature regarding no effects of acute static stretching immediately prior to sprint performance,5,11,20
but appears to contradict other studies where static stretching was shown to adversely affect sprint times.2,4,21
Because the authors were intent on investigating the acute effects of stretching, we focused our research on one major muscle group (the IP muscle), which has been described by previous authors in the literature to be one of the most important muscles involved in sprinting.16‐18
The protocol employed during the current study differs somewhat when compared to other studies found in the literature, in that, the authors of the current study measured the effects of stretching on a dynamic event immediately after stretching (0‐60 seconds), whereas other studies investigated the effects of stretching on performance approximately 3‐10 minutes following the performance of stretching.3,5,6,11,22,23
Contrary to other research, which included multiple muscles in the stretching protocol, the authors did not find a significant difference between pre‐ and post‐measures of 40‐yard sprint times when subjects were stretched using BS, DS, or SS methods.4‐6,11,20
In contrast to the current study, Winchester et al reported a 3% decrease in sprint performance for track and field athletes after participating in a static stretching protocol, which was conducted after a 30 minute dynamic warm‐up.5
Likewise, Fletcher et al reported an increase in 50‐m sprint time (decrease in sprint performance) in a group of competitive track and field athletes after passive static stretching, despite being combined with active dynamic stretching. Conversely, they observed a decrease in 50‐m sprint time (improvement in performance) after warm‐ups involving static dynamic stretches combined with active dynamic stretches or with the active dynamic stretches alone.11
Sim et al reported increases in 20‐m sprint times (decrease in sprint performance) when static stretching was performed after dynamic activities in the warm‐up, but found that static stretching followed by dynamic activities resulted in repeated sprint performance similar to that obtained when dynamic activities alone were performed.4
Little and Williams reported that a static‐stretch protocol produced significantly faster runs than did the no‐stretch protocol for the 20 m sprint.6
However, in their study, subjects performed further warm‐up activity after the stretching, which may have affected the immediate adverse effects of static stretching that have been previously reported. Vetter reported no changes on a 30‐m sprint after static stretching.20
The subjects in the current study showed significantly faster post 40‐yard sprint times when compared to pre 40‐yard sprint times only after the NS condition. One possible reason for this improved performance could be that the baseline sprint served as a dynamic warm‐up and dynamic warm‐ups without stretching have been reported to improve sport specific skills such as sprinting.24
As such, the rehearsal of specific movement patterns may have helped increase coordination of the subsequent sprint, especially in untrained recreational runners who did not use sprinting as a training method. McMillian et al revealed that warming the muscle up prior to an activity by engaging in dynamic warm‐up exercise facilitates physiological changes that may result in modest performance enhancement.25
They showed that dynamic warm‐up resulted in better performance scores on selected measures of power and agility (T‐shuttle run, underhand medicine ball throw for distance, and 5‐step jump) relative to static stretching warm‐up or no warm‐up.25
In the case of the NS group, the baseline 40‐yard sprint may have been enough to facilitate performance enhancement, thereby improving the post NS condition sprint time in the present study.
Another possible reason for improved performance in the NS condition could be that lack of stretching after a dynamic activity may have contributed to a stiffer tendon, which may have correlated with increased performance in force production.26
A possible reason for this mechanism was proposed by Wilson et al.15
The authors suggested that for concentric muscle actions, a stiffer musculotendinous system would improve contractile component force production, thus allowing more favorable length and velocity conditions. In other words, a stiffer musculotendinous unit should allow the contractile component to be at a more optimal point on both the force/velocity and force/length curve in terms of force production. Additionally, Rosenbaum et al concluded that stretching impaired force production and hypothesized that the decreased force production was due to mechanical changes such as increased tendon slack.26
Burkett et al pointed to neurophysiological changes as a potential reason for improved performance; their research suggests that warm‐ups increase power production and performance by activating neuromuscular functions.27
Other researchers have cited this phenomenon as post‐activation potentiation (PAP), which has been defined as the temporary increase in the contractile ability of muscles after a previous contraction session.28
One limitation of this study was the use of a small group of untrained, recreational, non‐competitive runners instead of trained runners. Consequently, it becomes important not to generalize the findings to competitive runners. Yet, the results of this study may be more relevant for trained runners than recreational runners due, in part, to stringent training regimens, warm‐up routines, and stretching protocols as well as potential differences in parameters such as height, weight, and BMI. Conversely, the findings from the present study may have value in generalizing to recreational runners commonly seen in physical therapy practice. Another limitation was soreness reported by the participants. Many of the participants complained of muscle soreness due to previous trials, and 10 participants cited muscular soreness as the reason for dropping out of the study. This may be related to the fact that the current subjects were recreational runners and therefore less accustomed to the higher muscular forces generated during sprinting than in other forms of running.
Future research should include the use of trained runners to see if these same effects are seen in these athletes as well. Further study might address the effects of stretching mode on return to sprinting activity among recreational runners, which is an important consideration when taking patients through a full spectrum of rehabilitation and the resumption of prior activity levels. Research could also be conducted to see if there are any differences between sexes and use of multiple trials examining the effects over time in each condition should be considered.