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Biomechanics/Neuromuscular

(1) NO EFFECT OF FATIGUING JOINT ANGLE ON TORQUE AND NEUROMUSCULAR RESPONSES FOLLOWING SUSTAINED, ISOMETRIC FOREARM FLEXION TASKS ANCHORED TO RPE

Thursday, July 13, 2023
12:00 PM – 1:30 PM East Coast USA Time
Location: Milano III-IV
Abstract Details: Ratings of perceived exertion (RPE) are a momentary representation of how easy or difficult a given task feels and are related to the level of effort, strain, discomfort, and fatigue experienced during exercise. Changes in pre-test to post-test maximal voluntary isometric contractions (MVIC) are used to assess the magnitude of strength loss due to a fatiguing task, which can be influenced by the psychological state, contractile function, and muscle activation.

Purpose: The purpose of this study was to examine the effects of the fatiguing joint angles (FJA) on MVIC and neuromuscular responses following sustained, isometric forearm flexion tasks anchored to RPE=8 (OMNI-RES 0–10 scale).

Methods: Nine men (mean±SD: age=20.7±1.2 yrs, hheight=182.4±5.7 cm, body mass=84.9±15.3 kg) performed 2, 3 s forearm flexion MVICs at elbow joint angles of 75° (JA75), 100° (JA100), and 125° (JA125) in random order before and after sustained, isometric forearm flexion tasks anchored to RPE=8 at fatiguing joint angles of 75° (FJA75) and 125° (FJA125). The amplitude (AMP) and mean power frequency (MPF) of the electromyographic (EMG) and mechanomyographic (MMG) signals were recorded from the biceps brachii. Normalized torque was divided by normalized EMG AMP to calculate neuromuscular efficiency (NME). A dependent t-test was used to determine mean differences for the time to task failure (TTF) between the FJAs. Separate 2 (Fatiguing Joint Angle: 75° vs. 125°) x 2 (Time: Pre-test vs. Post-Test) x 3 (MVIC Joint Angle: 75° vs. 100° vs. 125°) repeated measures ANOVAs and Bonferroni corrected post-hoc paired t-tests were used to compare mean differences for MVIC (Nm), NME, EMG AMP (µVrms), EMG MPF (Hz), MMG AMP (m∙s-2), and MMG MPF (Hz). Effect sizes for the post-hoc comparisons were determined using Cohen’s d.

Results: There were no significant mean differences in the TTF between FJA75 and FJA125 (mean±SD: 276.3±185.0 vs. 227.7±96.4 s, p=0.223, d=0.440). For MVIC, pre-test values (collapsed across Fatiguing Joint Angle and MVIC Joint Angle) were greater than post-test values (mean±SD: 51.9±5.4 vs. 46.2±6.0 Nm, p< 0.001, d=1.855). In addition, MVIC values (collapsed across Fatiguing Joint Angle and Time) indicated that the MVIC at JA75 was less than the MVIC at JA100 (mean±SD: 46.0±6.3 vs. 50.7±6.5 Nm, p=0.005, d=-1.261). For MMG AMP (collapsed across Time and MVIC Joint Angle), FJA75 was greater than FJA125 (mean±SD: 0.51±0.13 vs. 0.47±0.14 m∙s-2, p=0.019, d=0.980). For MMG MPF, follow-up pairwise comparisons (decomposed by MVIC Joint Angle) indicated no differences from pre-test to post-test at any of the MVIC joint angles (p=0.033 to p=0.868, d=-0.855 to d=0.248). There were no significant three-way interactions, two-way interactions, or main effects for EMG AMP, EMG MPF, or NME (p>0.05).

Conclusions: These findings suggested that the decreases in MVIC, without fatigue-induced changes in the neuromuscular parameters, were not dependent on the FJA and may not be related to changes in the motor unit activation strategies. PRACTICAL APPLICATIONS: Biceps brachii fatigability may not exhibit joint angle specificity, so pre-test to post-test measures may be compared between studies using different fatiguing joint angles. Furthermore, under some conditions, neuromuscular parameters may not be sensitive to fatigue that results in decreases in MVIC.

Acknowledgements: None.