Despite being common in the gym and on high school practice fields, the stretching debate rages on amongst rehabilitation professionals and researchers. It is a hot topic when I teach residency and continuing education courses to physical therapists.
Should we stretch prior to physical activity?
First, it depends on the intent of your stretching. If you are stretching to improve flexibility, you are going to be disappointed with long-term results. Current research suggests stretching primarily provides short-term improvements in mobility only. To be fair, long-term gains haven’t been studied extensively, but it appears a stretching program would have to be quite aggressive.
Our bodies are adaptive and responsive to the demands we regularly place on them. Gymnasts are not flexible because they stretch often, they are flexible because they move at extreme ranges of motion every day for years.
Movement is more effective at improving flexibility than status stretching. You don’t have to do gymnastics either; research shows weightlifting is as effective as stretching for improving flexibility.
Stretching doesn’t work as a warm-up either, however, it can still be useful as a pregame strategy on the psychological side. Some athletes use stretching as a time to center themselves and perform visualization exercises. If stretching is part of a pre-game routine and without it, you feel unprepared, go ahead and stretch.
There is a caveat.
Stretching may reduce strength and power output.
How stretching affects strength and power
When I first learned about the potential influence of stretching on strength and power, I immediately removed it from my clinical practice and spread the message to all my fellow physical therapists.
My actions were premature.
There are many ways to stretch and all do not result in strength and power deficits. A 2019 research review paper aimed to clear up some misconceptions and provide guidance.
If you perform a quick PubMed search, you will find many articles that recommend avoiding stretching prior to strength or power activities. Power is how quickly we can produce force while strength is the maximum force we can produce. The Olympics provide useful references.
Power examples: sprints (especially coming out of the blocks), long jump, triple jump, high jump, shot put, javelin, discus, hammer throw, Olympic weightlifting (the clean and jerk and snatching motions)
Strength examples: Olympic weightlifting (lifting the bar off of the ground and holding it overhead)
In most sports, power is more important than strength. Both rely on the response of the nervous system to the desired movement. The nervous system communicates to muscles through nerves and the nerves attach to muscles through motor units. The number of motor units present and their efficiency depend on the frequency and intensity of an athlete's training history (genetics plays a role too).
Immediately following static stretching, motor unit activation decreases in volume and velocity. This results in a slower muscle contraction (decreased power) and less force produced(decreased strength). Alterations in motor unit recruitment aren’t the only issue.
Muscle tendon unit stiffness is another factor that may improve strength and power output. While morning back stiffness is aggravating, muscle-tendon stiffness is desired. Stiffness allows for more force production.
Consider a spring versus a slinky. If you pull them apart and let go, which will recoil with more force and speed?
To maximize strength and power, we want to achieve ideal length-tension relationships. If you were to squat right now, where in the squat do you feel strongest? In the bottom, the middle, or the top? Each muscle has an ideal position when the most force can be developed.
Think about sprinters in the starting blocks. They adjust the position to place their knees and hips at ideal angles for their height. A middle ground of knee and hip bend is achieved to maximize their power out of the blocks.
Stretching changes that length-tension relationship. It doesn’t move the location of the ideal relationship, it diminishes the strength and power potential as the overall tension is reduced.
This is a short-term effect — about 5 minutes — but one that research suggests is very real.
The question we need to ask now is what type of stretching diminished power?
Don’t stretch aggressively
There is a common theme amongst research studies that show diminished strength and power following stretching: all stretches are uncomfortable.
Participants are instructed to stretch to the level of discomfort and maintain that position. I imagine the intention is to create adaptations in the mechanical properties of the muscles and tendons, but as mentioned earlier, those changes won’t last.
To make matters worse, the short-term improvements in flexibility are mirrored by short-term reductions in strength and power. How much strength and power are lost? That depends on how long you hold the stretch.
Keep stretches short
Our muscles don’t have internal clocks, counting down the time until they flip a strength or power switch, but there are noticeable trends with respect to dose relationships. It appears 60 seconds is the threshold for inducing strength and power deficits.
This study showed strength and power deficits after 120 seconds of stretching but not 30 or 60 seconds. Taking it a step further, this systematic review assessed 106 studies and found stretches that exceeded 60 seconds reduced muscle strength by 7.5% on average. Stretches less than 45 seconds had minimal effects — less than 2% — but they were not statistically significant.
A systematic review conducted four years later found similar results, with strength and power reducing by 4.6% after stretching more than 60 seconds.
Keep in mind, these effects don’t last forever. They are short-term changes as studies these studies assess strength and power immediately after the stretching routine.
Integrate stretching into warm-up routines
When I stated stretching is not an effective warm-up, I wasn’t saying stretching can’t be used in a warm-up routine.
For a warm-up to be effective, you need to increase body temperature. Static stretching does not accomplish this. But static stretching can provide time for visualization and psychological preparation.
When integrated into a dynamic warm-up routine, stretching has no negative effects on strength or power. Part of this may be a result of time passing and part may be a result of increased metabolic activity.
Maybe the stretching doesn’t help physically and it is net neutral. That’s fine if you gain the psychological benefits.
How this applies to athletes
As you noted, the effect sizes in these studies are small, meaning the impact on performance may not be noticeable. They only apply to strength and power performance as well.
If you are going for a long run, stretching won’t affect performance. If you are preparing for a weight training session at the gym that focuses on moderate repetition ranges to build muscle and endurance, stretching likely won’t impact you either. Where the impacts will be more noticeable are when small margins of error matter.
If you are entering a powerlifting contest, a few pounds may be the difference between winning and losing your weight class. If you have a track meet, stretching your hamstrings aggressively a few minutes before a 100m dash may cost you a shot at the podium.
These performance differences are small but noticeable in short-duration strength and power sports. The compound effect should be considered as well.
If you aggressively stretch before every heavy training session, small performance differences compound over time, potentially reducing the impact of your training. This is part speculation, however, as no studies have assessed a potential long-term impact of stretching on strength and power development.
So, what’s the takeaway?
If you want to stretch, then stretch, but understand what it is doing to your body. It isn’t an effective warm-up in isolation and it won’t improve flexibility long-term. It may help you prepare for an event psychologically, but if the event is strength or power-based, keep the stretching light, short-duration, and part of a more robust dynamic warm-up routine.