Relationship Between Hamstring Flexibility and Extensor Muscle Activity During a Trunk Flexion Task

Characteristics of electromyographic activity during yoga-applied stabilization exercises

BACKGROUND

Yoga exercise is widely performed as a treatment of low back pain and performance enhancement. Some yoga exercises are applied from general stabilization exercise (GSE) such as bridge exercises. The purpose of this study was to compare muscle activity during various types of GSE and yoga-applied stabilization exercise (YSE), and clarify characteristics of activity pattern during YSE.

METHODS

Fourteen healthy men participated in the study. We recorded muscle activity from the trapezius, trunk, and lower limb muscles using surface electromyography. The participants performed 5 front bridge exercises (elbow-knee, elbow-toe, high-plank, up-dog, down-dog), 2 back bridge exercises, 2 side bridge exercises, and 2 adductor side bridge exercises. The muscle activity was compared between GSE and YSE.

RESULTS

In comparison of muscle activity during the front bridge exercises, elbow-toe and down-dog produced the higher activation in the external oblique (EO), internal oblique (IO), gluteus medius (Gmed), and rectus femoris than the other exercises. The activities of the upper trapezius, lower trapezius (LTZ), erector spinae, EO, and IO during Y-back bridge (Y-; indicating yoga exercise) showed significantly higher than during back bridge. Y-adductor side bridge produced significantly higher activation in the LTZ, IO, gluteus maximum, and Gmed than adductor side bridge.

CONCLUSIONS

The results of front bridge exercise showed that down-dog enhanced the activity of abdominal and anterior hip muscles as well as elbow-toe. Furthermore, YSE activated more the trapezius, trunk, and gluteus muscles than GSE during the back bridge and adductor side bridge.

Differential Back Muscle Flexion-Relaxation Phenomenon in Constrained versus Unconstrained Leg Postures

Previous studies examining the flexion-relaxation phenomenon (FRP) in back muscles through trunk forward flexion tests have yielded inconsistent findings, primarily due to variations in leg posture control. This study aimed to explore the influence of leg posture control and individual flexibility on FRP in back and low limb muscles. Thirty-two male participants, evenly distributed into high- and low-flexibility groups, were recruited. Activities of the erector spinae, biceps femoris, and gastrocnemius muscles, alongside the lumbosacral angle (LSA), were recorded as participants executed trunk flexion from 0° to 90° in 15° increments, enabling an analysis of FRP and its correlation with the investigated variables. The findings highlighted significant effects of all examined factors on the measured responses. At a trunk flexion angle of 60°, the influence of leg posture and flexibility on erector spinae activities was particularly pronounced. Participants with limited flexibility exhibited the most prominent FRP under constrained leg posture, while those with greater flexibility and unconstrained leg posture displayed the least FRP, indicated by their relatively larger LSAs. Under constrained leg posture conditions, participants experienced an approximate 1/3 to 1/2 increase in gastrocnemius activity throughout trunk flexion from 30° to 90°, while biceps femoris activity remained relatively constant. Using an inappropriate leg posture during back muscle FRP assessments can overestimate FRP. These findings offer guidance for designing future FRP research protocols.