Abstract
Despite the rising interest in the use of portable force sensors during isometric exercises to inform on neuromuscular performance, the design of practical field-based methods to obtain reliable measures is an ongoing challenge. We aim at identifying the intra-session and test-retest reliability of a rapid, isometric knee extension test to evaluate the maximal voluntary concentric force (MVC), rate of force development (RFD) and impulse following a field-based approach. On two occasions, 14 athletes unfamiliar with the test completed three sets of 2 s ballistic contractions (as fast and hard as possible) with 30 s rest. Raw and filtered data were collected in real time using a portable force sensor. RFD and impulse were highly reliability during “late” phases of the contraction (0–250 ms) since the first session (coefficient of variation (CV) < 9.8%). Earlier phases (0–150 ms) achieved a moderate reliability after one familiarization session (CV < 7.1%). Measures at 0–50 ms did not reach sufficient reliability (CV~14%). MVC was accurately assessed. Dominant limbs were not importantly altered by the familiarization. In opposite, non-dominant limbs showed large variations. New evidence is provided about the positive effects of a single familiarization session to improve the reliability the isometric knee extension test for rapid force production assessment. Coaches and practitioners may benefit of from these findings to conduct practical and reliable assessments of the rapid force production using a portable force sensor and a field-based approach.
Highlights
Isometric strength of knee extensors has been widely assessed since decades due to its close relationship with functional performance [1,2,3] and as effective tool for monitoring injury rehabilitation success [4,5]
RFD0–50 was readable with a moderate reliability (CV ≤ 13.6% intraclass correlation coefficient (ICC) ≥ 0.941) in Session 2 with fitted signal
The main findings of this study indicate that: (i) rate of force development (RFD) and impulse during the isometric knee extension tests can be assessed with high reliability during “late” phases of the contraction (0–250 ms) since the first session, following a field-based approach, in young athletes unfamiliar with the test; (ii) earlier phases of the contraction (0–150 ms) can be measured with moderate reliability after one familiarization session; (iii) in contrast, measures at 0–50 ms requires larger sampling rates and/or longer familiarization to reach sufficient reliability; (iv) the results confirm previous findings that knee extension maximal voluntary concentric force (MVC) can be accurately assessed using portable force sensors [14,15]
Summary
Isometric strength of knee extensors has been widely assessed since decades due to its close relationship with functional performance [1,2,3] and as effective tool for monitoring injury rehabilitation success [4,5]. The use of the isometric knee extension exercise during explosive or ballistic contractions has attracted increasing attention as an effective method to test and improve force production during rapid muscle activation, with positive transfers to sport-specific performance such as jumping or sprinting [6,7,8]. Despite the rising interest in the use of isometric testing to determine improvements in ballistic sport-specific movements [6,7], the design of practical field-based methods to obtain reliable. The current study aimed to determine the intra-session and test-retest reliability of a rapid, isometric knee extension test to evaluate the MVC, RFD and impulse on both limbs in young athletes unfamiliar with the test, following a field-based approach. Based on the existing literature, we hypothesize that late contractions >250 ms would reach sufficient reliability since the first session, whilst earlier phases would require a previous familiarization
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