A study concluded that intensive stretching such as lower-body passive static stretching (PSS) should be avoided before training the lower body or performing the 1 repetition maximum (1RM) in the squat exercise in favor of an active dynamic warm-up (AD) using resistance training equipment in the lower-body musculature.

It investigated the acute effect of passive static stretching (PSS) of the lower-body musculature on lower-body strength in a 1 repetition maximum (1RM) squat exercise in young (18-24 years.) moderately trained men (n = 17).

Two supervised warm-up treatments were applied before each performance testing session using a counterbalanced design on nonconsecutive days. The first treatment consisted of an active dynamic warm-up (AD) with resistance machines (i.e., leg extension/leg flexion) and free weights (i.e., barbell squat), whereas the second treatment added PSS of the lower body plus the AD treatment.

One repetition maximum was determined using the maximum barbell squat following a progressive loading protocol.
Subjects were also asked to subjectively evaluate their lower-body stability during 1RM testing sessions for both the AD and PSS treatments. A significant decrease in 1RM (8.36%) and lower-body stability (22.68%) was observed after the PSS treatment.

Plausible explanations for this observation may be related to a more compliant muscle tendon unit and/or altered or impaired neurologic function in the active musculature. It is also possible that strength was impaired by the PSS because of joint instability.

Gergley JC. J Strength Cond Res. 2013 Apr;27(4):973-7. doi: 10.1519/JSC.0b013e318260b7ce.
Department of Kinesiology and Health Science, Human Performance Laboratory, Stephen F. Austin State University, Nacogdoches, Texas.