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.

(1) Background: ‘Slope’ refers to the position faced by golfers on the course. Research on the recruitment strategies of thoracolumbar erector spinae during golf swings on different slopes may help us to understand some underlying mechanisms of lower back pain. (2) Purpose: The purpose of the present study is to assess electromyography (EMG) patterns of the erector spinae muscles (ES) and the kinematics of the trunk and swing parameters while performing golf swings on three different ground slopes: (1) no slope where the ball is level with the feet (BLF), (2) a slope where the ball is above the feet (BAF), and (3) a slope where the ball is below the feet (BBF). Furthermore, the present study evaluates the effect of slope on the kinematics of the trunk, the X-factor angle, and the hitting parameters. (3) Methods: Eight right-handed recreational male golfers completed five swings using a seven-iron for each ground slope. Surface electromyograms from the left and right sides of the ES thoracolumbar region (T8 and L3 on the spinous process side) were evaluated. Each golf swing was divided into five phases. Kinematics of the shoulder, trunk, and spine were evaluated, and the ball speed, swing speed, carry, smash factor, launch angle, and apex were measured using Caddie SC300. (3) Results: The muscle activity of the BAF and BBF slopes was significantly lower than that of the BLF slope during the early follow-through phase of the thoracic ES on the lead side (i.e., left side) and during the acceleration and early follow-through phases of the lumbar ES on the lead side. The lead and trail side (i.e., right side) lumbar ES were more active during acceleration than the thoracic ES. Additionally, the trends of the lead and trail sides of the thoracolumbar regions on the three slopes were found to be the same across the five phases. Trunk angle and X-factor angles had no significant differences in address, top of backswing, or ball impact. The maximum separation angles of the X-factor appeared in the early phase of the downswing for all the three slopes. Regarding smash factor and launch angle, there were no significant differences between the three slopes. The ball speed, swing speed, carry, and apex were higher on BLF than on BAF and BBF slopes. (4) Conclusion: The findings suggest that amateur golfers face different slopes with altered muscle recruitment strategies. Specifically, during the acceleration phase of the golf swing, the BAF and the BBF slopes, compared with the BLF slope, significantly underactivated the lead side thoracolumbar erector spinae muscles, thereby increasing the risk of back injury. Changes in muscle activity during critical periods may affect neuromuscular deficits in high-handicap players and may have implications for the understanding and development of golf-related lower back pain. In addition, the X-factor angle was not affected by the slope, however, it can be found that the hitting parameters on the BLF slope are more dominant than on the other slopes.