Effect of Reformer Spring Resistance Modifications on Core Muscle Activity During Basic Core Muscle Exercises

Background: Core muscles serve as a central group within the functional kinetic chain, stabilizing the spine during movement. The Reformer is one of the most popular and primary pieces used in Pilates core exercises, requiring effective control of core muscles. The purpose of this study was to investigate the effect of Reformer spring resistance on core muscle activity. Method: 18 healthy adult females (age: 29.83 +/- 4.22 years, body height: 164.98 +/- 4.14 cm, body mass: 53.67 +/- 5.32 kg) participated in this study. Surface electromyography was recorded from six muscles: rectus abdominis, internal oblique, erector spinae, multifidus, rectus femoris, and biceps femoris during core exercises. Participants performed three core exercises (hip roll, knee-off, and elephant) under three different Reformer spring conditions (fixed platform, platform connected to springs with moderate resistance, platform connected to springs with low resistance). Results: During the hip roll exercise, mean muscle activity of the rectus abdominis, erector spinae, multifidus, and biceps femoris was significantly increased on the low-resistance spring platform compared to the moderate-resistance platform and fixed platform conditions (p < 0.001). During the knee-off exercise, mean muscle activity of the rectus abdominis, internal oblique, erector spinae, and multifidus significantly increased on the low-resistance platform compared to the fixed platform (p < 0.001). Furthermore, during the elephant exercise, mean muscle activity of the rectus abdominis, internal oblique, and rectus femoris significantly increased on the low-resistance spring platform compared to the fixed platform (p < 0.001). Conclusions: These findings suggest the unstable platform caused by the Reformer spring modification impacts core muscle activity during basic core exercises. Therefore, when designing core exercise programs using the Reformer, platform instability should be considered a key factor for rehabilitation and core stability.