Study of Reliability and Validity of the Load Cell-Type Hand Dynamometer Compared to the Jamar Dynamometer and the Number of Reliable Grip Strength Measurements.

Background: Standardised measurement protocols for grip strength remained unclear due to variations in values depending on the device and measurement method. The load cell hand dynamometer has recently been developed. This study aims to investigate the reliability of the load cell dynamometer by comparing it to the Jamar dynamometer, which is considered the gold standard, and to identify a reliable and practical measurement method. Methods: This study included 80 healthy hospital workers (mean age of 40.1 years). All measurements were performed seated, with the elbow flexed 90° and the grip span at the second handle (approximately 50 mm) for the Jamar dynamometer, and with the elbow extended and the grip span fixed at 55 mm for the load cell dynamometer. Grip strength was measured three times on each hand using two dynamometers, and the same tests were repeated on different days. Test-retest reliability, the association between the two devices and the agreement between the two measurement methods were assessed using the intraclass correlation coefficient (ICC), Pearson correlation and the Bland-Altman analysis. Results: The ICC of the one measurement was lower than that of three measurements for both dynamometers, but was above 0.858 in all groups, indicating sufficient reliability with one-time measurement. Additionally, the ICC for different days revealed good reliability (Jamar: >0.830, load cell: >0.772). The load cell dynamometer showed significantly lower values in all measurements despite the excellent correlation (r > 0.70) and the agreement between the two dynamometers. Conclusions: This study revealed sufficient reliability of the load cell dynamometer with the standardised measurement method, but it should be noted the lower values compared to the Jamar dynamometer. Additionally, one-time measurement reliability is adequate for practical use by standardising the measurement methods for both dynamometers. Level of Evidence: Level III (Diagnostic).

Impact of the contraction of medial forearm muscles during grip tasks in different forearm positions on medial support at the elbow joint.

We measured the medial joint distance (MJD), activity of muscles involved in medial elbow-joint support, and grip strength, aiming to examine the supportfunction of muscles. MJD was measured in supinated and pronated positions of the forearm of 10 participants under three conditions: at rest (R), under valgus load on the elbow joint (L), and under valgus load on the elbow joint during the grip task (L-grip). Under the L-grip condition, electromyography was performed on flexor digitorum superficialis (FDS), pronator teres (PT), flexor carpi radialis (FCR), and flexor carpi ulnaris (FCU); subsequently, normalized integrated electromyograms (NIEMG) were calculated. Under the L-grip condition, MJD was shorter in the pronated position than in the supinated position (p < 0.001); however, grip strength was lower in the pronated position. NIEMG of FDS was 90% in both positions, and those of FCR and FCU were low at 10%. However, that of PT was 3.6% in the supinated position and 40.9% in the pronated position, showing higher NIEMG in the pronated position (p < 0.001). Medial support during grip tasks was higher in the pronated position probably because PT activity compensates for the decreased FDS activity.