The Influence of Verbal Instruction on Measurement Reliability and Explosive Neuromuscular Performance of the Knee Extensors

The Reliability and Magnitude of Time-Dependent Force-Time Characteristics During the Isometric Midthigh Pull Are Affected by Both Testing Protocol and Analysis Choices

ABSTRACT

Guppy, SN, Kotani, Y, Brady, CJ, Connolly, S, Comfort, P, and Haff, GG. Title: The reliability and magnitude of time-dependent force-time characteristics during the isometric mid-thigh pull are impacted by both testing protocol and analysis choices. J Strength Cond Res 36(5): 1191-1199, 2022-This study aimed to investigate whether the use of short-duration (SHORT) isometric midthigh pull (IMTP) trials resulted in greater reliability and magnitude of time-dependent force-time characteristics than traditionally performed IMTP trials (TRAD). Fourteen subjects with >6 months' training experience with the power clean volunteered to take part in the study. Subjects performed five ∼1-second IMTP trials (SHORT) and five 5-second IMTP trials (TRAD). SHORT resulted in substantially more reliable rate of force development (RFD) measures (intraclass correlation coefficient [ICC] = 0.97-0.99; coefficient of variation [CV] = 2.6-7.0%), particularly during time bands from force-onset to 150 ms, compared with TRAD when trials were selected for analysis based on peak force (ICC = 0.66-0.83; CV = 14.1-38.5%). Selecting TRAD trials based on RFD0-200 resulted in similar reliability compared with SHORT of those same epochs (ICC = 0.97-0.99; CV = 2.5-7.8%). Furthermore, SHORT resulted in significantly greater force at specific time points, RFD, and impulse compared with TRAD trials (p = 0.001-0.033; g = -0.16 to -0.66). Based on these results, strength and conditioning professionals should use specific testing protocols (i.e., TRAD and SHORT) depending on the component of an athlete's force-generating capacity that they wish to assess and remain aware of the effect analysis choices they have on the reliability of IMTP force-time characteristics.

Does Performance-Related Information Augment the Maximal Isometric Force in the Elbow Flexors?

The effects of different feedback conditions on the elbow flexors maximal voluntary isometric (MVIC) force were examined. In a single visit, twenty participants (10 males) were exposed to four conditions including, Visual only; (i.e., knowledge of results [VI]); Verbal encouragement (i.e., verbally stating pull, pull [VE]); VI and VE (VIVE); and no VI or VE (NOVIVE). Three, 5-s MVIC trials were completed for each condition. Separate 2 × 4 (sex × condition) repeated measures analyses of variance (ANOVA) were used to examine MVIC force, rate of force development (RFD₂₀₀), and rate of electromyography (EMG) rise (RER₂₀₀) for the 0-200-ms window. There was a significant main condition effect for MVIC force (p < 0.001). Significantly greater MVIC force was shown for VIVE compared to VE (p < 0.001) and NOVIVE (p = 0.002) conditions, and VI compared to VE (p = 0.011) and NOVIVE (p = 0.009) conditions. A significant sex × condition interaction (p = 0.036) was observed for RFD₂₀₀, with significantly (p = 0.003) greater RFD₂₀₀ in males compared to females, in the VI condition only. There were no significant differences in RFD₂₀₀ among condition for males (p = 0.033) or females (p = 0.194). There was a significant main effect for sex (p = 0.006) for RER₂₀₀, with significantly greater (p = 0.003) RER₂₀₀ (conditions merged) in males (mean ± standard deviation (SD): 422.99 ± 124.67%), compared to females (220.68 ± 134.01%). Here we suggest the importance of providing VI feedback alone, or in conjunction with VE, for the measurement of elbow flexion MVIC. Additionally, these results provide a foundational framework for future studies aiming to improve feedback modalities during training or rehabilitation.

Transcutaneous electrical nerve stimulation improves fatigue performance of the treated and contralateral knee extensors

PURPOSE

Transcutaneous electrical nerve stimulation (TENS) can reduce acute and chronic pain. Unilateral fatigue can produce discomfort in the affected limb and force and activation deficits in contralateral non-exercised muscles. TENS-induced local pain analgesia effects on non-local fatigue performance are unknown. Hence, the aim of the study was to determine if TENS-induced pain suppression would augment force output during a fatiguing protocol in the treated and contralateral muscles.

METHODS

Three experiments were integrated for this article. Following pre-tests, each experiment involved 20 min of TENS, sham, or a control condition on the dominant quadriceps. Then either the TENS-treated quadriceps (TENS_Treated) or the contralateral quadriceps (TENS_Contra) was tested. In a third experiment, the TENS and sham conditions involved two\; 100-s isometric maximal voluntary contractions (MVC) (30-s recovery) followed by testing of the contralateral quadriceps (TENS_Contra-Fatigue). Testing involved single knee extensors (KE) MVCs (pre- and post-test) and a post-test 30% MVC to task failure.

RESULTS

The TENS-treated study induced greater (p = 0.03; 11.0%) time to KE (treated leg) failure versus control. The TENS_Contra-Fatigue induced significant (p = 0.04; 11.7%) and near-significant (p = 0.1; 7.1%) greater time to contralateral KE failure versus sham and control, respectively. There was a 14.5% (p = 0.02) higher fatigue index with the TENS (36.2 ± 10.1%) versus sham (31.6 ± 10.6%) conditions in the second fatigue intervention set (treated leg). There was no significant post-fatigue KE fatigue interaction with the TENS_Contra.

CONCLUSIONS

Unilateral TENS application to the dominant KE prolonged time to failure in the treated and contralateral KE suggesting a global pain modulatory response.