Ladder-climbing resistance training stimulates upper limb flexor digitorum profundus muscle hypertrophy in rats

Skeletal muscles have notable features that enable muscle hypertrophy in response to resistance training (RET). Most animal studies on ladder climbing have focused on the lower limb muscles; however, the movement also involves the upper limb muscles. Moreover, little evidence exists regarding whether RET affects food intake. Therefore, this study aimed to investigate RET-induced muscle hypertrophy in both the upper and lower limb muscles and to examine changes in food intake.

Twenty male Wistar Hannover rats (6 weeks old) were randomly assigned to sedentary control (SED, n = 10) or resistance training (RET, n = 10) groups during a 2-week acclimatization period. RET rats underwent the primary exercise training for 8 weeks, after 1 week of climbing adaptation, with a one-repetition maximum test. Body weight and food intake were monitored weekly. Twenty-four hours after the final training session, major muscles were dissected and weighed, and the flexor digitorum profundus (FDP) was analyzed using the cross-sectional area (CSA) of the myofibers.

RET group showed significantly decreased final body weight and food intake compared to the SED group (p < 0.001). RET enhanced both muscle quantity (increased relative FDP muscle weight) and quality (improved muscle strength capacity and larger FDP myofibers).

Ladder-climbing RET induced hypertrophy in the upper limb FDP muscle rather than in other lower limb muscles despite decreases in body weight and food intake. Upper extremity strength training can provide benefits to healthy adults and individuals with limited lower extremity mobility.