Measuring what matters in isometric multi-joint rate of force development

The difference between several neuromuscular tests for monitoring resistance-training induced fatigue

The purposes of this study were to investigate the acute effects of resistance training protocol on kinetic changes in squat jump (SJ), shortened isometric mid-thigh pull (IMTP), and isometric squat (ISQ) and to examine the relationship of dynamic maximum strength with performance changes over 48 hours in resistance-trained individuals. Participants completed performance tests at pre-, post-24 hours, and post-48 hours resistance training protocol (Baseline, Post24, and Post48). The training protocol consisted of 5 sets of 10 repetitions of back squat (BSQ) at 60% of 1 repetition maximum (1RM). SJ variables included jump height (JH), peak power (PP), and relative PP. For the IMTP and ISQ, isometric peak force (IPF), relative IPF, rate of force development at 250 milliseconds (RFD250), and impulse at 250 milliseconds (IMP250) were calculated. Significant decreases were observed from Baseline to Post24 (p = 0.023, Cohen's d_z effect size [d_z] = 1.00) and Post48 (p = 0.032, d_z = 0.94) in SJ JH. IMTP IMP250 significantly decreased from Baseline to Post48 (p = 0.046, d_z = 0.88). Significant negative correlation was found between relative 1RM BSQ and the changes from Baseline to Post48 in ISQ RFD250 (p = 0.046,r = -0.61). Acute performance decreases might remain until 48 hours after resistance training in explosive strength and impulse regardless of isometric testing type.

Rate of Force Development as an Indicator of Neuromuscular Fatigue: A Scoping Review

Because rate of force development (RFD) is an emerging outcome measure for the assessment of neuromuscular function in unfatigued conditions, and it represents a valid alternative/complement to the classical evaluation of pure maximal strength, this scoping review aimed to map the available evidence regarding RFD as an indicator of neuromuscular fatigue. Thus, following a general overview of the main studies published on this topic, we arbitrarily compared the amount of neuromuscular fatigue between the “gold standard” measure (maximal voluntary force, MVF) and peak, early (≤100 ms) and late (>100 ms) RFD. Seventy full-text articles were included in the review. The most-common fatiguing exercises were resistance exercises (37% of the studies), endurance exercises/locomotor activities (23%), isokinetic contractions (17%), and simulated/real sport situations (13%). The most widely tested tasks were knee extension (60%) and plantar flexion (10%). The reason (i.e., rationale) for evaluating RFD was lacking in 36% of the studies. On average, the amount of fatigue for MVF (−19%) was comparable to late RFD (−19%) but lower compared to both peak RFD (−25%) and early RFD (−23%). Even if the rationale for evaluating RFD in the fatigued state was often lacking and the specificity between test task and fatiguing exercise characteristics was not always respected in the included studies, RFD seems to be a valid indicator of neuromuscular fatigue. Based on our arbitrary analyses, peak RFD and early phase RFD appear even to be more sensitive to quantify neuromuscular fatigue than MVF and late phase RFD.

Utility of a Shortened Isometric Midthigh Pull Protocol for Assessing Rapid Force Production in Athletes

Suarez, DG, Carroll, KM, Slaton, JA, Rochau, KG, Davis, MW, and Stone, MH. Utility of a shortened isometric midthigh pull protocol for assessing rapid force production in athletes. J Strength Cond Res XX(X): 000-000, 2020-The purpose of this investigation was to determine the magnitude of difference, reliability, and relationship to performance of a shortened isometric midthigh pull (IMTP) protocol. Fourteen strength-trained men (age: 26.8 ± 5.0 years, height: 176.3 ± 6.9 cm, body mass: 86.8 ± 13.9 kg, and training age: 8.5 ± 6.9 years) performed 1-second (SHORT) and traditional (TRAD) IMTP protocols during consecutive weeks. Peak force (PF), instantaneous force (90 & 200 ms), rate of force development (RFD) (0-90 ms & 0-200 ms), and impulse (0-90 ms & 0-200 ms) from each protocol were collected. Paired samples t test and Hedge's g were calculated to determine the magnitude of difference in each variable between protocols. Within-session and between-session reliability was assessed with intraclass correlation coefficient, coefficient of variation, and 95% confidence intervals. Static jumps were performed to compare relationships of the IMTP variables from each protocol with jumping performance. There was no statistically significant (p > 0.05) difference in PF between the protocols (p = 0.345; g = -0.07). All early force-time variables were significantly higher in the SHORT protocol (p = <0.001-0.018; g = 0.38-0.79). The SHORT protocol resulted in more reliable RFD measures within-session. Correlations with jumping performance were mostly similar between protocols (r = 0.253-0.660). The SHORT IMTP protocol resulted in comparable PF values and considerably higher early force-time characteristics despite a restrained time to produce force and shorter rest. The SHORT protocol allows for an accurate assessment of rapid force-generating abilities while necessitating shorter collection periods than typical IMTP protocols.