Intrasession and Intersession Reliability of Isometric Squat, Midthigh Pull, and Squat Jump in Resistance-Trained Individuals [Article Review]

Introduction

This article by Ishida et al. addresses a critical topic for sports scientists and strength and conditioning professionals: the reliability of commonly used performance tests—namely, the isometric squat (ISQ), isometric midthigh pull (IMTP), and squat jump (SJ)—in moderately resistance-trained men. By evaluating both intrasession (within the same session) and intersession (between separate sessions) reliability, the study aims to clarify which kinetic variables are most consistent and how well these assessments correspond to dynamic performance, particularly the 1 repetition maximum (1RM) back squat.

Key Takeaways and Results

The study enlisted 11 moderately resistance-trained men, conducting familiarization, then a battery of tests (SJ, shortened IMTP, ISQ) separated by a week, with robust control over training variables to minimize confounds. Reliability was assessed using intraclass correlation coefficients (ICC) and coefficients of variation (CV), with thresholds established for reliability (ICC≥0.80, CV≤10%).

Key findings:

• Squat Jump (SJ): All kinetic variables (body mass, jump height, peak force, peak power) were highly reliable both within and between sessions (ICC 0.91–1.00, CV 0.5–9.1%).

• Isometric Midthigh Pull (IMTP) and Isometric Squat (ISQ): Isometric peak force (IPF) and impulse at 200 and 250 milliseconds demonstrated reliable results for both intrasession and intersession comparisons (ICC 0.90–0.99, CV 2.1–8.1%). RFD at early time points (RFD90 and RFD200) did not achieve reliability standards.

• Correlations: ISQ peak force showed a statistically significant large correlation with 1RM back squat (r=0.63, p=0.038), indicating ISQ's strong relevance to dynamic strength in this population. The shortened IMTP peak force had only a moderate (non-significant) correlation with squat strength (r=0.50, p=0.11), and squat jump measures did not correlate significantly with 1RM squat.

  
  

The authors discuss potential reasons for these findings, such as the specificity of the ISQ to the squat movement and shortened IMTP protocol potentially failing to capture true peak force due to limited contraction time.

Conclusion and Practical Applications

In summary, this study provides strong evidence that the squat jump, shortened IMTP, and isometric squat tests—when executed under controlled protocols—offer reliable measures of lower-body power and strength characteristics in moderately resistance-trained men. Of the three, the ISQ peak force stands out as the most robust indicator of dynamic squat performance, likely due to its greater movement specificity.

Practical application:

• Practitioners can confidently use shortened IMTP and ISQ (especially ISQ peak force and impulse) to monitor training-induced neuromuscular adaptations, with reliable measurements across repeated testing sessions.

• These tests can be implemented every few weeks to assess performance changes and adjust training programs, while minimizing both time commitment (<20–30minutes per athlete) and measurement error.

• Changes greater than 8.5% for ISQ and shortened IMTP may be considered practically meaningful, allowing coaches to respond dynamically to athletes’ progress or fatigue.

• The careful selection of test protocols—especially joint angles and contraction duration—is essential for accurate evaluation and meaningful interpretation of results.

  
  

This work underscores the importance of reliable testing batteries for athlete monitoring and points to the ISQ peak force as a preferred metric for tracking maximal strength adaptations in resistance-trained individuals.

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