Stretching the truth
A timely receipt of a research paper on the impact of stretching (Baxter et al, 2015) coincided with a coach-education question last week. Therefore, I thought that I would round up what has now become a recent trilogy on athlete recovery by adding my thoughts on stretching to that of the transition period (see August 2018) and rest & recovery (December 2018).
As those who regularly read my missives will know, I tend to support my arguments with terms such as ‘evidence based’ or, where no empirical evidence exists and arguments are supported by intuition or assumption, as ‘evidence inspired’. One of the more obvious examples of the latter is the argument for using stretching as a tool to aid performance or reduce the risk of injury in endurance athletes, and now we have a paper that sheds some further light on this subject.
Historically, pre-exercise stretching was the staple of endurance running groups, prescribed by coaches to prepare the limbs for exercise. Post-exercise stretching was also prescribed as part of a cool down programme to minimise the effects of delayed onset muscle soreness (DOMS). For simplicity, stretching could then be described as being one of two kinds – acute stretching referring to discrete exercises conducted immediately prior to exercise (Wallmann, et al., 2012) or chronic stretching, conducted as part of a long-term strategy for increasing flexibility (Stone, et al., 2006). Due to the limited time available here, for now I will simply focus on acute stretching programmes and may return to chronic stretching at a later date.
Flexibility has long been recognised as a component of fitness (Bompa & Haff, 2009) and arguably stretching has been considered to be an appropriate if not important part of that strategy (Shrier, 2004; Wilson et la., 2010). However, evidence shows that elite endurance runners are anything but flexible, with studies suggesting that they tend to be less flexible than their amateur counterparts (Saunders et al., 2004). Whilst this statement appears to be at best counter-intuitive, research has shown that untrained people with the lowest levels of flexibility have the most economic running styles (Gleim et al., 1990). Although this study needs repeating across a broader range of athlete ability, it does support the findings of several other theories.
Increased mobility of the pelvis over the transverse and frontal planes during the stance phase of running requires an excessive energy cost to stabilise the pelvis. Certainly sprinters are renowned for extolling the benefits of having tense muscles and tendons to increase elastic storage and thus reduce oxygen demand. It has also been proposed that reduced flexibility could be accounted for by the hypertrophy of muscle resulting in a reduced range of joint motion. All good food for thought and certainly all worthy of additional study.
However, we do know that acute stretching prior to exercise as part of a warm up regime has been shown to decrease running economy (reflecting the energy demand of running at? a constant submaximal speed) (Saunders et al., 2004; Shrier, 2004; Thacker et al., 2003). The rationale for this theory is that stretching reduces the mechanical efficiency of the lower body through the reduction of musculotendinous stiffness (Thacker et al, 2003). In this instance, musculotendinous stiffness ‘specifically refers to the [muscle] unit’s ability to resist an applied change in length’ (Kuitunen et al., 2002).
Historically, muscular stiffness has been associated with increased risk of injury and an inhibitor of athletic movement particularly in the early stages of an event and yet, in endurance runners muscular stiffness is recognised as a desirable trait (Wilson & Flanagan, 2008). Inflexibility in the hip and calf regions are associated with improved running economy (Baxter et al., 2015). The ‘reduction of mechanical efficiency stems directly from the decrement of muscle stiffness that appears as a result of muscle stretching’ (Baxter et al., 2015). As we have postulated in our own research concerning running form, stiffer muscles around the ankle and knee cause an ‘increase in force potentiation when transitioning from the braking to the push off phase in running’ (Kyrolainen & Komi, 1994).
More effective elastic energy storage and return from a stiffer musculotendinous system is therefore favoured in endurance running (Gleim, et al., 1990). Without taking advantage of muscular stiffness, activation of increased numbers of motor units requires increased oxygen consumption and energy expenditure (Wilson et al, 2010). Additionally, acute stretching may strain muscles, causing a decrease in force development and an increase in oxygen requirement immediately following the stretching regime (Shrier, 2004).
All interesting stuff, but the research is not all negative. Some studies have identified that stretching isolated muscle groups prior to performance testing can increase the strength of that muscle group, (Akagi & Takahashi, 2014), however, as yet, there is no evidence to suggest that the same applies to endurance running (Worrell, et al., 1994).
Thus, according to the academic studies, not only is there no recognised benefit to acute stretching as part of a warm up activity prior to running, but there would appear to be disadvantages to doing so, not least to running economy through decreases in mechanical efficiency and increases in oxygen demand. However, whilst this evidence based theory makes academic sense, our own intuition on this topic which is associated with our experience of immobility, would suggest that some other strategy needs consideration. Also, this still leaves the question of whether there is an optimum level of flexibility required to maximise running efficiency. According to Saunders et al (2004), optimum flexibility is a balance between muscle stiffness to optimise elastic energy storage and return, whilst allowing for an optimal stride length (Saunders et al., 2004). I await with bated breath their definition of the optimum stride length because this is, of course, related to running form.
Whatever your current strategy, if it is working for you – minimising the risk of injury and maximising performance – then at this juncture I would advise that you continue to follow your plan but keep a watchful eye on future research. At some point in the near future, I will hope to follow this up with a brief look at chronic stretching strategies.
In the meantime, please go carefully in this weather and take no risks with your training. We have a full season of training and racing ahead, and so swapping the road bike for the turbo trainer or doing shorter running sessions at submaximal pace over the next few days, will minimise the risk whilst allowing you to stay active. A few days of power and heating outages at work have put us under great time pressure this month and we go into February with some outstanding work. Therefore, we have reduced the number of athlete bookings this month to allow for some consolidation and catch up. If you are awaiting reports or testing dates, please be patient and we hope to be back up to speed shortly.
One date that is confirmed is a further swim video analysis session at Tiddenfoot on Saturday 9th February at 12:00. More details on request.