Definitive guide to flexibility series. Part 1 - Stretching and subsequent performance
Stretching and subsequent performance. Part 1: important caveats for avoiding unwanted effects
A common assumption made against using stretching for athletic populations is that it reduces force output and therefore leads to a reduction in sports performance. However, as is often the case when coming to any conclusion from reviewing research is that the answer is far more complex and is dependent on many contextual factors. This post is going to explore this topic further and highlight certain variables involved that determine the acute effects experienced.
Although there is some literature that demonstrates negative effects from acute stretching, this certainly does not paint the whole picture of what the evidence states about this topic (1). Such studies suggest that stretching will dampen force output due to reduction in neural drive and/or acute biomechanical alterations to the muscle-tendon that impede the length-tension relationship (2, 3). However, when we look at the specific protocol and population used as that will provide us with valuable information about why there is such variability in outcomes with this topic.
For these studies, there are similar characteristics, namely that the participants are unfamiliar/untrained to stretching and that the protocols used include prolonged static stretching (generally > 180 seconds). This raises two some important questions:
1. What acute impact does stretching acutely have on untrained vs trained individuals (i.e. have had previous exposure to stretching)?
2. During a typical warm-ups how long do people stretch for (and therefore is clinically relevant)?
The first question is very important to tease out as the simple understanding of previous exposure to a stimulus greatly influences the short-term neurophysiological response to it. Namely, it greatly influences how much fatigue (i.e. lessened capacity for work) is experienced and therefore how much recovery is needed in order to return to a baseline level of fitness or enhancement of physical output. These principles relate to a well-known phenomenon called post-activation potentiation (PAP) that is commonly used to assist with rehabilitation and enhancing physical capacity (4). PAP is based on the understanding that using a physical conditioning stimulus typically at a maximal or near maximal intensity enhances both peak performance and rate of force development. The realisation of PAP are dependent on individual characteristics related to the potentiating stimulus in that those who have an increased capacity of the related biomotor ability had a larger positive response to performance in a shorter period of time (i.e. less recovery time) (5).
In other words, if you’re familiar with a training stimulus you are less likely to experience negative effects from it and you will recover from it more quickly. This aligns with literature around stretching and acute performance changes as generally studies that found a short-term decrement is only realised for less than 10 minutes (6). Additionally, previous exposure to stretching demonstrated an increase in power performance at 4 minutes post static stretching (which notably went for 90 seconds total) had a positive increase in countermovement jump at four minutes following the conditioning activity (7). In short, the acute response of stretching is dependent on your previous exposure. Familiarising yourself with a particular mechanical stimulus mitigates the initial ‘shock’ that the central nervous system experiences to a novel activity. In comparison, think about the acute effects from the first time you completed resistance training - there is a high level of fatigue perceived! Clinically speaking, when it comes to stretching it makes sense to expose your system to it outside of a training session initially to ‘familiarise’ yourself before implementing it into a warm-up that target areas of restriction or open up related myofascial chains related to the sporting movement.
Another important element that needs to be highlighted is the use of stretching in an integrated warm-up. Practically speaking, stretching is not used in isolation prior to athletic performance even though this is how many of the studies are set-up. A recent study explored the effect of different stretching protocols as a part of a comprehensive warm-up in young male team sports athletes (8). This study found that stretching on physical function had no different effect to not stretching at all. Again this is a very valuable finding, because it emphasises that in the context of a typical warm-up (i.e. not using stretching alone) stretching does not impede performance, regardless of whether static, dynamic or no stretching was used. Interestingly, prior to completing the study participants were asked what protocol would impede performance the most with the majority choosing static stretching – talk about unfounded cultural beliefs.
In summary, stretching can be used safely and effectively as a part of an integrated warm-up. I believe there is a lot more work to be done in this field, particularly with exploring certain stretch variables namely training history and intensity. For now, be assured that it is possible to include stretching in your warm-up without it negatively affecting your performance.