Author(s): YANG, Y., WANG, H., LIN, C., LIN, Y., CHENG, C., Institution: NATIONAL TAIWAN NORMAL UNIVERSITY, Country: TAIWAN, Abstract-ID: 239

INTRODUCTION:
Critical load (CL) represents the lower boundary required to recruit type II muscle fibers in the early phase of strength training. Traditional approaches for determining CL or critical power (CP) typically necessitate multiple testing trials, thereby limiting their applicability. The 3-min all-out test has been employed across various exercise modalities to estimate CP or its analogues within a single session. However, this methodology has not yet been adapted for resistance exercises. Therefore, this study aimed to evaluate the validity and reliability of a 3-min all-out squat test (3MST) for estimating CL and CP, utilizing data obtained from an inertial measurement unit (IMU) and a linear position transducer (LPT).
METHODS:
Following the determination of one repetition maximum (1RM), ten well-trained males (squat relative 1RM: 2.4 ± 0.3 times body mass) underwent three traditional repetition-to-failure tests at 45%, 55%, and 65% of 1RM. Critical load (CLTRAD) and critical power (CPTRAD) were derived from force/power–repetition, force/power–reciprocal repetition, and work–repetition relationships, where force was calculated using barbell load and power output was obtained through LPT. Participants then performed two 3MSTs at 20% 1RM. End-test metrics, defined as the average of the last five repetitions, included mean propulsive force/power for IMU (ELIMU/EPIMU) and peak force/mean power for LPT (ELLPT/EPLPT).
RESULTS:
ELIMU, ELLPT, EPIMU, and EPLPT demonstrated excellent test-retest reliability, with intra-class correlation coefficients ranging from 0.96 to 0.98 (p < 0.05). CLTRAD significantly correlated with ELIMU and ELLPT (r = 0.86–0.98, p < 0.05). Bland–Altman analysis indicated that ELIMU (40 ± 8 kg, 22 ± 2%1RM, coefficient of variation [CV%]: 9–18%) and ELLPT (43 ± 10 kg, 24 ± 3%1RM, CV%: 18–27%) tended to overestimate CLTRAD (32 ± 12 to 36 ± 14 kg, 18 ± 5 to 20 ± 6%1RM). No significant difference existed between ELIMU and CLTRAD, while ELLPT was significantly higher than CLTRAD, which was based on force–repetition and work–repetition models (p < 0.05). Similarly, CPTRAD significantly correlated with EPIMU and EPLPT (r = 0.70–0.77, p < 0.05). However, Bland–Altman plots revealed that EPIMU (183 ± 76 W, CV%: 73–78%) and EPLPT (169 ± 67 W, CV%: 66–71%) substantially overestimated CPTRAD (81 ± 32 to 85 ± 37 W). EPIMU and EPLPT were significantly higher than CPTRAD (p < 0.05).
CONCLUSION:
The 3MST administered using portable devices constitutes a time-efficient and cost-effective approach with the potential to predict CLTRAD. The limited predictive accuracy of EPIMU and EPLPT for CP might be attributed to the heavier load and slower movement velocity characteristic of traditional methods, in contrast to 3MST. Future studies with larger sample sizes are required to determine the validity of 3MST in predicting CL. Supported by National Science and Technology Council, Taiwan (NSTC 113-2410-H-003-152-MY2 and 114-2424-H-003-007-DR). Contact: andescheng@ntnu.edu.tw