Stretching before the training session: do you lose strength?

Should you stretch before lifting? A long static stretch, one minute or more per muscle, makes you lose a few percent of strength right after. Short, or slipped into a real warmup, it changes almost nothing. And in no major trial did it prevent injuries. Before a bodybuilding session, it can even cost you repetitions. Here is what twenty-two studies measure.

What stretching does to your strength, right after

A 2013 meta-analysis gathered trials on static stretching done before exertion, the kind where you hold the position without moving. Right after, strength drops by an average of 5.4%, power by 1.9% and explosive performance by 2.0%. The authors conclude that static stretching, used alone as a warmup, is to be avoided.

A 2016 review compares techniques: static stretching lowers performance by an average of 3.7%, stretching with contraction (called PNF) by 4.4%, whereas dynamic stretching, done in motion, improves it by 1.3%.

Everything comes down to duration

The same review shows it: held for 60 seconds or more, static stretching costs 4.6% of performance; less than 60 seconds, only 1.1%. A 2012 review finds the same progression: no net effect below 30 seconds (−1.1%) or between 30 and 45 seconds (−1.9%), a likely drop from 60 seconds onwards. A 2019 review speaks of a "trivial" effect, from 1 to 2%, up to 60 seconds per muscle group, and from 4 to 7.5% beyond.

In 10 men, 60 seconds of hamstring stretching dropped their maximum strength to 262 N, compared to 288 N without stretching, whereas 30 seconds changed nothing significant. But not all trials agree: in 16 trained men and women, stretches of 15 or 30 seconds were already enough to lower hamstring strength, and duration did not change the magnitude of the loss. Conversely, in 10 active adults aged 40 to 60, ten minutes of stretches held for 30 seconds changed nothing for the jump and improved balance.

In a real warmup, the effect disappears

Many trials test stretching alone, right before measurement. This is not what you do in the gym. In 20 team sport athletes, static stretches of 5 or 30 seconds, or dynamic stretches, integrated into a complete warmup changed nothing for the sprint, the jump or changes of direction, while the athletes expected to perform better by stretching. In 10 active men, five minutes of running before and after short stretches (six times six seconds) gained range of motion for 30 minutes, without loss of performance: the jump was even higher 1 and 10 minutes after.

Replacing static stretching with a movement-based warmup pays off more: in 30 officer cadets, the dynamic warmup improved the shuttle run, medicine ball throw and jump compared to the warmup with static stretches and no warmup. The 2011 review therefore recommends a simple order: light aerobic activity, then high-amplitude dynamic stretches, then movements specific to your sport.

Before bodybuilding: fewer repetitions

On maximal strength in a single trial, the effect is small. Over an entire session, it can matter. In 12 trained men, only stretching with contraction reduced maximum load on the leg press (−5.5%), but all three stretching techniques lowered the number of repetitions in the session: −20.8% after static stretching, −17.8% after ballistic (jerking) stretching, −22.7% after stretching with contraction, and the total volume accordingly. In 9 men, static and ballistic stretches also yielded fewer repetitions for the lower body than a specific warmup.

Other trials see nothing: in 15 men, 30 seconds of stretching per muscle did not change the number of repetitions on four sets of bench press at 80% of maximum load; in 15 American football players, low or high volume stretches, included in a dynamic warmup, did not modify the maximum load on the bench press. To know your work loads, the 1RM calculator estimates them from a set.

A major trial qualifies the picture: in 2,377 adults, stretching 30 seconds per muscle group before and after sport did not reduce the overall risk of injury, but slightly reduced troublesome soreness (24.6% against 32.3%) and injuries to muscles, ligaments and tendons. The 2016 review, for its part, sees no clear effect of stretching on injuries. For soreness, see also soreness: what to do.

And over weeks of training?

Stretching before each training session does not appear to hinder your progress. In 45 young untrained men, 80 seconds of static or dynamic stretching before each weight training session for eight weeks neither added nor removed strength or muscle from the hamstrings. An eight-week trial in 32 students even finds greater strength gains with stretching, in leg extension (+27% vs. +14%) and leg press (+31% vs. +9%), but this is an isolated trial in beginners. To find out if stretching makes muscle grow, see does stretching make a muscle grow?.

In summary

In practice: start your training session with a few minutes of light activity and warm-up sets of your first exercise, save long static stretches for another time, and if you insist on stretching beforehand, stay under 60 seconds per muscle. To build your training sessions with their exercises, the training session generator takes care of it, and the exercise library details each movement.

Every figure in this article comes from a study you can open: the underlined mentions lead to the summary of the work it is taken from, written based on the abstract alone. The trials are small and often conducted on a single training session, mostly in young, athletic adults. Informative content, which does not replace the advice of a healthcare professional.