The Acute Effects of a Cycling Warm-Up With and Without Foam Rolling on Biceps Femoris Stiffness and Tissue Homogeneity

ABSTRACT: Earp, JE, Joshi, L, Mathisen, C, Robinson, D, Rehbein, CO, Kraemer, WJ, and Peñailillo, L. The acute effects of a cycling warm-up with and without foam rolling on biceps femoris stiffness and tissue homogeneity. J Strength Cond Res XX(X): 000-000, 2026-Biceps femoris (BFLH) strains are common athletic injuries that are influenced by the muscle's mechanical properties. Proximal-to-distal variation in muscle stiffness impairs load sharing and increases focal strain in the proximal region, where strain injuries are most likely to occur, and is believed to contribute to injury risk. Therefore, understanding the effects of specific warm-up activities on BFLH intramuscular stiffness and homogeneity is warranted. Twenty-one healthy active subjects performed a bilateral cycling warm-up followed by a unilateral foam rolling intervention (CYL + FR) or cycling alone (CYL). Changes in proximal-, middle-, and distal-BFLH passive intramuscular stiffness were assessed through shear wave elastography at 15, 30, 45, 60, 90, and 120 minutes post-CYL and CYL + FR. Changes in overall and regional stiffness were compared between conditions using a 2 × 3 × 7 (Condition × Region × Time) mixed model ANOVA. Muscle stiffness decreased in both conditions (CYL: -1.349 ± 0.436 kP, CYL + FR: -1.095 ± 0.65 kP, p = 0.004) to a similar magnitude (p = 0.707), and no condition by time effect was observed (p = 0.480). However, proximal-BFLH stiffness decreased to a greater extent in CYL than CYL + FR (mean difference: -1.486 ± 0.629 kP, p = 0.028), but no differences were observed in the middle (p = 0.548) or distal regions (p = 0.216). Although foam rolling did not enhance or prolong changes in muscle stiffness, it did mitigate increases in stiffness heterogeneity that resulted from CYL in a pattern that would improve load sharing and reduce focal strain in the proximal-BFLH. Future work should examine whether promoting stiffness homogeneity through preactivity foam rolling translates to reduced hamstring strain incidence during subsequent activity.