The general category of intervention described in the post is self-myofascial release (SMR), most often studied using foam rollers and roller massagers rather than tennis balls.

On range of motion, the evidence is reasonably consistent. A systematic review with multilevel meta-analysis found that foam rolling significantly improved hip and knee range of motion across conditions, with benefits persisting for at least 10 minutes, no notable differences between pressure levels, and no effect of sex on the magnitude of improvement. A separate meta-analysis concluded that foam rolling increases range of motion and appears useful for recovery from exercise induced muscle damage, with no detrimental effect on other athletic performance measures, though apart from range of motion it cannot be concluded that foam rolling directly produces the other claimed benefits.

On soreness and recovery, the evidence is weaker and mixed. One meta-analysis reported that

foam rolling had small and moderate intervention effects on muscle soreness.

A controlled comparison found the opposite for treatment of existing soreness:

no significant between-group differences at 24 or 48 hours in pain, fatigue, or skin surface temperature, with the authors concluding that soft tissue mobilisation applied with a foam roller or percussive massage device does not seem superior to passive resting for alleviating DOMS in recreational athletes.

On mechanism, the "release" framing is not supported. A narrative review of rolling mechanisms concluded that there is insufficient evidence to support that the primary mechanisms underlying rolling and similar devices are the release of myofascial restrictions, and thus the term "self-myofascial release" is questionable , with proposed mechanisms instead involving

activation of cutaneous and fascial mechanoreceptors and interstitial type III and IV afferents that modulate sympathetic and parasympathetic activation, activation of global pain modulatory systems, and reflex-induced reductions in muscle and myofascial tone. A 2025 systematic review of chronic effects noted that one study reported five weeks of SMR improved range of motion alongside increased tissue elasticity and elevated pain thresholds, suggesting range of motion improvements may be mediated more by altered pain perception than structural tissue changes, and a second study observed increased range of motion in the untreated contralateral limb without corresponding reductions in that limb's muscle stiffness. Independent practitioner commentary summarising this literature notes that rolling one leg can decrease muscle pain and increase flexibility in the untreated opposite leg, indicating the range of motion increase is mostly due to increased stretch tolerance via global pain modulatory responses.

Relevant to the hip specifically, one trial of duration effects found that

pressure pain threshold and knee flexion range of motion increased for up to 20 and 60 minutes respectively after rolling, and tissue hardness decreased for up to 60 minutes. A randomised trial in piriformis syndrome directly comparing approaches exists:

63 participants aged 20 to 40 were randomised to a piriformis stretch group, a self-myofascial release group, or a control group, all on a 4-week strengthening home programme, with pain intensity as the primary outcome and hip range of motion as secondary. I was unable to retrieve its numerical results within this session.

Claims about tennis balls specifically on the glutes are carried almost entirely by commercial and blog sources. One such page asserts that evidence suggests the tennis ball method can temporarily stretch and relax the gluteal muscles, reducing piriformis-related pain without professional tools , but it cites no study and refers vaguely to a "study-like approach."