Background The lumbar multifidus (LMF) muscle, which is involved in the mechanical stability of the lumbar spine, reportedly undergoes atrophy in patients with low back pain. Preventing or mitigating low back pain requires strengthening the LMF muscle; however, methods for triggering selective and significant contraction of this muscle have not been fully studied. This study aims to clarify how, in the hands-and-knees or standing position, the position of the arm and leg on one side affects the activity of the lumbar erector spinae (LES) and LMF muscles. Methods We recruited nine adult men with no prior history of low back pain. Measurements were taken in four different postures under varying conditions (that is, one arm and one leg were lifted in either the hands-and-knees or standing position,) as follows: (1) shoulder joint flexion and hip joint extension in the hands-and-knees position; (2) 90° shoulder joint abduction and hip joint abduction in the hands-and-knees position; (3) shoulder joint flexion and hip joint extension in the standing position; and (4) 90° shoulder joint abduction and hip joint abduction in the standing position. The 90° shoulder joint abduction involved simultaneous horizontal abduction, while the hip joint abduction involved simultaneous extension. Muscle activity of the LES and LMF in each posture was measured using a surface electromyograph. Results Muscle activity of the LMF was significantly higher in 90° shoulder joint abduction and hip joint abduction than in shoulder joint flexion and hip joint extension in both the hands-and-knees and standing positions. The LES muscle showed no significant differences in activity between each posture. Conclusions The results suggest that unilateral 90° shoulder joint abduction and contralateral hip joint abduction in the hands-and-knees and standing positions may produce selective and significant contraction of the LMF muscle.

[Purpose] This study aimed to clarify the characteristics of movement when lifting loads at defined stance widths, and the associated mechanical stress in the lumbar region. [Subjects and Methods] Eight healthy, male university students lifted a 10kg load placed on the floor using three stance widths. High-speed cameras and surface electromyography were used to measure body movements and muscle activities.[Results] Anterior tilt angle of the trunk and activity of the lumbar paraspinal muscles were significantly decreased when using a wide stance. There were no significant differences in the activities of the lower extremity muscles.[Conclusion] These results suggest that use of a wide stance while lifting loads decreases the anterior tilt angle of the trunk and the activity of the lumbar paraspinal muscles, which would decrease mechanical stress on the lumbar region.

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[Purpose] To investigate the effects of quadriceps setting in different positions on quadriceps femoris muscle activity. [Subjects and Methods] Ten healthy males performed single-leg quadriceps setting in the supine and prone positions. Single-leg quadriceps setting in the prone position was performed with the hip on the non-supported side either extended at 0° or maximally extended. Surface electromyography was used to measure the muscle activities of the rectus femoris, vastus medialis, and vastus lateralis on the supported side during single-leg quadriceps setting.[Results] The activity of the rectus femoris muscle was significantly increased by single-leg quadriceps setting in the prone position with the hip maximally extended on the non-supported side.[Conclusion] The results suggest that performing single-leg quadriceps setting in the prone position with the hip maximally extended on the nonsupported side increases the activity of the rectus femoris muscle on the supported side.

BackgroundOf the shoulder external rotators, the infraspinatus and teres minor are the key muscles that contribute to the dynamic stability of the shoulder. It is crucial to properly measure the strength values to evaluate muscle function and training load for shoulder external rotators. A suspension scale (SPS) can measure the mass of the suspended object, and it may be possible to apply it to measure strength. However, the utility of strength measurements using an SPS has not been clarified in previous studies. In this study, we aimed to investigate the intra-rater reliability of measuring the strength of shoulder external rotators using an SPS and the relationship between strength measurement using an SPS and a handheld dynamometer (HHD). MethodologyThe participants were 10 healthy males with 20 shoulders (24.5 ± 2.5 years old; height = 172.8 ± 5.4 cm; weight = 69.6 ± 8.1 kg). Upper extremity strength was measured at 90° shoulder abduction, 90° external rotation, 0° horizontal adduction/abduction, 90° elbow flexion, and 0° forearm pronation/supination in the prone position. The isometric strength of shoulder external rotation was measured with the SPS and HHD, and one examiner measured the maximum strength value. The intra-rater reliability of the two methods using SPS and HHD was evaluated using the intraclass correlation coefficient (ICC 1,2 ), standard error of measurement (SEM), minimum detectable change (MDC), and Bland-Altman analysis. The relationship between the SPS and HHD was calculated as the correlation coefficient between the strength values of SPS and HHD. ResultsThe intra-rater reliability of the strength measurement of shoulder external rotators using SPS was ICC 1,2 0.98 (95% confidence interval = 0.95-0.99), and SEM and MDC were 0.3 and 0.9, respectively. The measurements using SPS had no fixed and proportional biases. A significant positive correlation was observed between SPS and HHD (r = 0.94, p < 0.01). ConclusionsThe SPS is an alternative to the HHD for measuring the strength of shoulder external rotators. Thus, measuring the strength of shoulder external rotators using an SPS may be applied as a cost-effective and portable assessment method for shoulder function.