The Science of Stretching


by Dr. Reed Ferber, Ph.D. CAT(C)

Runners often have a lot of questions about stretching, such as: should I warm up first before I stretch? Will stretching improve my performance? Does stretching really help prevent injuries? These are all excellent questions and the answers can sometimes seem a bit confusing.

Let’s start with the physiological response to stretching. Just how does a muscle increase its length and become more flexible? The muscle-tendon unit contains an active (contractile) and passive (non-contractile) component. The active component is related to the muscle fibres, whereas the passive components consist of the connective tissues within the muscle and the muscle tendons. A single bout of stretching has its main effect on the passive components and increases muscle flexibility through elongation of the connective tissue and muscle tendons. However, by engaging in a regular stretching routine, over the span of several weeks or months, a muscle will become more flexible and increase its length primarily through the active component by adding muscle fibres to the ends of the muscle itself.

When should I stretch?
Stretching before a run is beneficial with respect to preparing your muscles and tendons for the run ahead. After a run, some light stretching assists with cooling down. However, if you want to make significant gains in muscle flexibility, you must stretch at a completely different time from your run. Researchers have shown that runners who only stretch prior to and following a run demonstrate the same amount of muscle flexibility over an eight-week program. However, runners who stretched at least four hours before or after their regular runs demonstrated significant gains in muscle flexibility over the same time span. This makes sense if you consider the sequence of events. First, stretching prior to a run will result in elongation of the connective tissue and muscle tendons. Second, the muscle will undergo tissue shortening during the run. Finally, stretching after the run will return the muscle to its pre-run length. Thus, no change in length of the muscle has been achieved and no consistent chronic stimulus has been provided to the muscle. However, stretching at a completely different time will provide sufficient stimulus and result in increased muscle flexibility.

Should I warm up before I stretch?
It has been shown that increasing the muscle temperature prior to stretching relaxes the passive component of the muscle to a greater degree and thus allows for greater elongation. In fact, an increase of only 1oC in muscle temperature is necessary for greater elongation and flexibility. Therefore, it is a good idea to partake in some type of gentle warm-up prior to stretching. However, this statement really only applies to stretching a muscle that has been doing little activity for the past several hours, such as in the morning after a night’s sleep. Since it is recommended that runners stretch at a completely different time from running, you should stretch at the end of the day and prior to going to sleep since your muscles have been generally active all day and you are not stretching “cold.”

Will stretching improve my performance?
There has been quite a lot of research done on this topic. It has been concluded that a regular stretching routine will improve muscle force production and jump height. However, the effects on running speed are contradictory, as some studies show improvements while others show decreases in sprint speed following single bouts of stretching. In addition, there is some controversy in the research related to whether or not regular stretching improves running economy during long runs. However, most of the studies have found slight improvements in running economy after a regular and long-term stretching routine. Therefore, if you’re looking for that personal best in the upcoming race season, keep training and stretch, stretch, stretch!

Will stretching reduce my injury risk?
There is strong evidence to show that regardless of your flexibility level, stretching does not decrease the likelihood of developing a running-related injury. It has also been widely reported in the past few years that there is no evidence to suggest that either static or dynamic stretching performed before or after exercise (or in an acute or chronic capacity) had the ability to reduce the severity or duration of muscle damage. In other words, muscle damage is caused by overloading the tissues. Stretching alone cannot reverse this damage nor prevent it from occurring. The best advice here is to stick to your plan and avoid training errors, which are widely accepted as the most common cause of a running injury.





Dr. Reed Ferber is the director of the Running Injury Clinic, a world leader in running-related research and 3D gait analysis technology. For more information, visit

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