Can stretching negatively affect running economy in endurance athletes

What is Running Economy

Running economy is a complex, multifactorial concept that comprises a number of physiological and biomechanical factors such as metabolic adaptations, a more efficient running gait which reduces braking forces and excessive vertical oscillation, and muscle and tendon stiffness[1]. The concept of running economy was introduced by Hill et al. in 1924. They hypothesized that, as we become more efficient in running, the metabolic cost of running at any given velocity would be reduced. (Quinn, Manley, Aziz, Padham, MacKenzie, 2011)

Though this is not yet fully understood, improving one’s running economy may help improve running capability. It has been reported that running economy can vary by as much as 30% among trained runners with similar VO2max. (Barnes & Kilding, 2015)

Flexibility

In this article, we will look at how stretching may affect running economy through musculotendinous unit (MTU) stiffness.

At the same time, flexibility is often viewed as an important component of physical fitness and is frequently promoted as a way to increase sports performance and lower risk of injury. This, however, contradicts with how MTU stiffness aids running economy. Moreover, studies have shown that there is no correlation between flexibility and reduction in risk of injury, and it may be deleterious to performance and decrease power (Mojock, Kim, Eccles and Panton, 2011).

To top that off, there are ?ndings from two investigations into the relationship between running economy and ?exibility (Gleim, Stachenfeld, Nicholas, 1990; Craib, Mitchell, Fields, Cooper, Hopewell, Morgan, 1996), suggest that inflexibility in certain areas of the musculoskeletal system may enhance the running economy in sub-elite male runners[6], and was associated with a decreased steady-state VO2 for treadmill walking and jogging[12]. These could be interpreted by some as a recommendation or caution against improving ?exibility.

As the effects of stretching may have on one’s running economy remain unclear, the aim of this review is to identify if stretching can negatively affect running performance, and whether there are any potential benefits to stretching.

Musculotendinous unit stiffness and running economy

Studies have shown that inflexibility in certain areas of the musculoskeletal system may enhance running economy (Craib et al., 1996). This can be explained as during the stretch-shortening cycle where elastic energy is stored in the Achilles tendon and reutilization of energy during the push-off phase in running[18, 19, 20]. Because both muscle and tendon properties may be important in this transfer of energy during human locomotion. Stored energy in these springs (muscle and tendon) could conceivably reduce muscle activation and spare energy expenditure, thus improving running economy. (Dumke, McBride, Pfaffenroth and McCauley, 2010).

Areas that seem to have shown to have the most impact on running economy are lower body extremity such as ankle dorsiflexion, hip rotation, and hamstring [3 – 6].

A particular study measures joint flexibility of the ankle and hip to determine the effect of leg stiffness and joint ranges of motion in the lower extremity on running economy. It concluded that running economy was not strongly related to vertical stiffness or hip ranges of motion, but was clearly influenced by ankle flexibility.[9]

Exercise-induced tendon stiffness and running economy

A 14-weeks study was conducted to find out if the running economy was affected by exercise-induced changes in triceps surae tendon stiffness and muscle strength [13].

The research found out that the exercise group saw a significant ～4% reduction in the rate of oxygen consumption and energy cost, which indicates a significant increase in running economy (Albracht, K., Arampatzis, A., 2013). They concluded that the increase in tendon stiffness and muscular contractile strength of the triceps surae MTU resulting from an exercise intervention has the potential to enhance running economy.

This further supports the idea that MTU stiffness contributes to an improvement in running economy is most possibly a result of the energy-efficient function of the elastic components in the muscles and tendons during the stretch-shortening cycle, thus improving running economy (Trehearn and Buresh, 2009).

Male & Female Athletes

Of the relatives of elite male and female runners who are of equal VO2max, we can conclude that males are more economical in both common velocities and relative intensities of running. (Daniels and Daniels, 1992). As it is believed that women have been shown to be less stiff than their male counterparts (Mojock, Kim, Eccles and Panton, 2011), a study was conducted to find out the effects of static stretching on running economy and endurance performance during treadmill running in trained female runners.[7]

Interestingly, this study did not find any significant effect on running economy or distance performance. However, it should be noted that no performance or injury prevention improvements have been seen after acute bouts of static stretching. Therefore, to maximize effectiveness in pre-performance, static stretching should be phased out of current programs and not added to future training programs. (Mojock, Kim, Eccles and Panton, 2011)

Age

A study was conducted in 2011 to find out the relationship between running economy and ageing. When compared to the Young (18-39 Years old) and Master (40-59 Years old) group, the study found that even though the older group (Age over 60 Years old) have a few areas of physical traits that decline with age, such as lower VO2Max, muscle mass and, reduction in flexibility. They did not detect intergroup differences in the running economy. Differences observed in running performance may be caused by other factors such as a decline in maximal and submaximal cardiovascular and hemodynamic variables and changes in muscle power. [Quinn, Manley, Aziz, Padham, MacKenzie, 2011]

This study mentions that running mechanics can be affected considerably from decreased flexibility, particularly with regard to step length and step frequency, 2 major factors of running velocity.[15]

Findings

Most studies support the idea that either stretching may negatively affect an individual’s running economy or tendon stiffness may lead to an improvement in running economy[3,4,5,7,8]. However, there are a few studies that fail to support the existence of an inverse relationship between flexibility and running economy. One study that was done back in the late 90s shows that that flexibility actually improved running performance [10]. Although this study shows that stretching improved running economy, the study population was limited to subjects with tight hip flexor or extensor muscles. (Shrier, I. 2004)

Another 10-weeks study shows no difference between the control and the stretch group[2], it is important to note that the study did not exclusively target the exact joint actions (dorsi?exion and stand-ing hip rotation) which Craib et al. (1996) showed to have the highest correlation with running economy. Thus, it is possible that ?exibility was increased only at the measured site and not at any other site. (Nelson et al., 2001)

This study uses a Sit-and-Reach test to measure flexibility. Since the Sit-and-Reach test measures the hamstring, hips, and lower back flexibility, it fails to test ankle dorsiflexion.

Conclusion

All things considered, it is still unclear whether stretching will definitely negatively affect the running economy, but studies seem to be heavily suggesting that it is so. However, it also appears that there is an optimal range of motion for runners. While the effects of stretching on the running economy remain unclear, it seems that stretching does not present any potential benefits to endurance runners, unless it is affecting step length and step frequency. But it’s worth mentioning that there might be the negative psychological impact of altering pre-competition routines which may outweigh any possible benefit associated with removing stretching from their warm-up. (Mojock, Kim, Eccles and Panton, 2011)

Reference

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