Similar performance fatigability and neuromuscular responses following sustained bilateral tasks above and below critical force

No sex differences in time-to-task failure and neuromuscular patterns of response during submaximal, bilateral, isometric leg extensions

BACKGROUND

In general, it has been suggested that females are more fatigue-resistant than males, with the magnitude of difference being most pronounced during low-intensity sustained contractions. However, the mechanisms for the apparent sex difference have not yet been fully elucidated in the literature. This study aimed to examine sex-related differences in fatigability and patterns of neuromuscular responses for surface electromyographic (sEMG) and mechanomyographic (sMMG) amplitude and frequency (MPF) characteristics during a sustained submaximal bilateral, isometric leg extension muscle action.

METHODS

A sample of 20 young recreationally active males and females with previous resistance training experience performed a sustained, submaximal, bilateral isometric leg extension until task failure. Time-to-task failure was compared using a nonparametric bootstrap of the 95% confidence interval for the mean difference between males and females. Additionally, patterns of response for sEMG and sMMG amplitude and MPF of the dominant limb were examined using linear mixed effect models.

RESULTS

There were no differences in time-to-task failure between males and females. Additionally, neuromuscular responses revealed similar patterns of responses between males and females. Interestingly, sEMG amplitude and sMMG amplitude and MPF all revealed non-linear responses, while sEMG MPF demonstrated linear responses.

CONCLUSION

These data revealed that time-to-task failure was not different between males and females during sustained submaximal bilateral, isometric leg extension. Interestingly, the parallel, non-linear, increases in sEMG and sMMG amplitude may indicate fatigue induced increases in motor unit recruitment, while the parallel decreases in sMMG MPF may be explained by the intrinsic properties of later recruited motor units, which may have inherently lower firing rates than those recruited earlier.

The Effects of Anchoring a Fatiguing Forearm Flexion Task to a High vs. Low Rating of Perceived Exertion on Torque and Neuromuscular Responses

ABSTRACT

Ortega, DG, Housh, TJ, Smith, RW, Arnett, JE, Neltner, TJ, Schmidt, RJ, and Johnson, GO. The effects of anchoring a fatiguing forearm flexion task to a high versus low rating of perceived exertion on torque and neuromuscular responses. J Strength Cond Res 38(5): e219-e225, 2024-This study examined the torque and neuromuscular responses following sustained, isometric, forearm flexion tasks anchored to 2 ratings of perceived exertion (RPE). Nine men (mean ± SD: age = 21.0 ± 2.4 years; height = 179.5 ± 5.1 cm; body mass = 79.6 ± 11.4 kg) completed maximal voluntary isometric contractions (MVIC) before and after sustained, isometric, forearm flexion tasks to failure anchored to RPE = 2 and RPE = 8. The amplitude (AMP) and mean power frequency (MPF) of the electromyographic (EMG) signal 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 assess the mean difference for time to task failure (TTF). Repeated-measures analysis of variances was used to compare mean differences for MVIC and normalized neuromuscular parameters. There was no significant difference in TTF between RPE = 2 and RPE = 8 (p = 0.713). The MVIC decreased from pretest to posttest at RPE = 2 (p = 0.009) and RPE = 8 (p = 0.003), and posttest MVIC at RPE = 8 was less than that at RPE = 2 (p < 0.001). In addition, NME decreased from pretest to posttest (p = 0.008). There was no change in normalized EMG AMP or EMG MPF (p > 0.05). The current findings indicated that torque responses were intensity specific, but TTF and neuromuscular responses were not. Furthermore, normalized EMG AMP and EMG MPF remained unchanged but NME decreased, likely due to peripheral fatigue and excitation-contraction coupling failure. Thus, this study provides information regarding the neuromuscular responses and mechanisms of fatigue associated with tasks anchored to RPE, which adds to the foundational understanding of the relationship between resistance exercise and the perception of fatigue.

Sustainability and perceptual responses during handgrip holds to failure at two fatigue thresholds

PURPOSE

Critical force (CF) provides an estimate of the asymptote of the force-duration curve and the physical working capacity at the rating of perceived exertion (PWCRPE) estimates the highest force that can be sustained without an increase in perceived exertion. Handgrip-related musculoskeletal disorders and injuries derived from sustained or repetitive motion-induced muscle fatigue are prevalent in the industrial workforce. Thus, it is important to understand the physiological mechanisms underlying performance during handgrip specific tasks to describe individual work capacities. This study examined prolonged, isometric, handgrip exercises by comparing the relative force levels, sustainability, and perceptual responses at two fatigue thresholds, CF and PWCRPE.

METHODS

Ten women (26.5 ± 3.5 years) performed submaximal, isometric handgrip holds to failure (HTF) with the dominant hand at four, randomly ordered percentages (30, 40, 50, and 60%) of maximal voluntary isometric contraction (MVIC) force to determine CF and PWCRPE. Isometric handgrip HTF were performed at CF and PWCRPE. Time to task failure and RPE responses were recorded.

RESULTS

There were no differences in the relative forces (p = 0.381) or sustainability (p = 0.390) between CF (18.9 ± 2.5% MVIC; 10.1 ± 2.7 min) and PWCRPE (19.5 ± 7.9% MVIC; 11.6 ± 8.4 min), and the RPE increased throughout both holds at CF and PWCRPE.

CONCLUSION

It is possible that complex physio-psychological factors may have contributed to the fatigue-induced task failure. CF and PWCRPE may overestimate the highest force output that can be maintained for an extended period of time without fatigue or perceptions of fatigue for isometric handgrip holds.

Coactivation does not contribute to fatigue-induced decreases in torque during reciprocal, isokinetic muscle actions

BACKGROUND: Studies of coactivation have typically utilized single movement isometric or isokinetic fatiguing muscle actions. OBJECTIVE: The purpose of the current study was to examine coactivation of the biceps brachii (BB) and triceps brachii (TB) in response to a maximal, reciprocal, isokinetic fatiguing task of the forearm flexors and extensors at slow (60∘/s) and moderate (180∘/s) isokinetic velocities in men. METHODS: Ten men (mean ± SD: age = 21.6 ± 1.3 years) completed 50 consecutive, maximal, reciprocal, isokinetic muscle actions of the right forearm flexors and extensors at 60 and 180∘/s. The amplitude (AMP) and mean power frequency (MPF) contents of the electromyographic (EMG) and mechanomyographic (MMG) signals from the BB and TB were recorded simultaneously throughout the fatiguing task. Repeated measures ANOVAs with Tukey post hocs were used to determine mean differences for the torque and neuromuscular parameters across repetitions. RESULTS: The torque analyses indicated greater fatigability at 180∘/s, compared to 60∘/s (p= 0.02). There were no significant changes in EMG AMP for either muscle during flexion or extension at 60∘/s (p> 0.05). At 180∘/s, there were significant increases in agonist EMG AMP (p= 0.01 to 0.004), however, no changes in antagonist EMG AMP (p> 0.05). For EMG MPF, there were significant decreases during flexion and extension (p< 0.001 to p= 0.02) at both velocities, collapsed across Muscle. There were no significant (p> 0.05) changes across repetition for MMG AMP or MPF. CONCLUSIONS: This study indicated velocity-specific responses to fatigue, with a greater magnitude of fatigability at 180∘/s. Furthermore, despite increases in EMG AMP of the agonist muscles at 180∘/s only, it was not sufficient to alter the ratio of coactivation, likely due to common neural drive between muscles. Thus, the decreases in torque in the present study were not attributable to increases in coactivation.

Which Frequency of Ankle Pump Exercise Should Be Chosen for the Prophylaxis of Deep Vein Thrombosis?

Introduction

Ankle pump exercise (APE) is an effective method to prevent deep vein thrombosis (DVT) in the lower extremities. However, traditional APE at a frequency of 3 times/min applied in the clinic lacked high compliance, and individuals were found to prefer an APE of 30 times/min. This study aimed to compare the effects of APEs with the above two different frequencies on the venous hemodynamics and fatigue of lower extremities.

Methods

The study applied a randomized cross-over design, and 307 healthy adults were randomly assigned into two groups, whose left feet performed 5 minutes of traditional APE (3 times/min, after 10 minutes of rest) and 5 minutes of selected APE (30 times/min, after 10 minutes of rest) in different orders. The diameters and blood flow velocities of the external iliac vein, femoral vein, and popliteal vein of the left extremities were recorded with the color doppler ultrasound when participants were at rest and after 5 minutes of traditional or selected APE. The fatigue of lower extremities was assessed with the Rating of Perceived Exertion (RPE) after the participants performed 5 minutes of different APEs.

Results

After both traditional APE and selected APE, the diameters and blood flow (peak systolic) velocities of the external iliac vein, femoral vein, and popliteal vein increased significantly in the participants (P<.01), and the effects of the two APEs on venous hemodynamics of the lower extremities had no significant difference (P>.05). However, participants reported that traditional APE caused higher fatigue, and 252 (82.1%) participants preferred APE at 30 times/min.

Conclusion

Both traditional and selected APE could increase venous blood flow in the lower extremity. Despite the equivalent effects, the selected APE of 30 times/min may cause less fatigue than the traditional one of 3 times/min.

Sex differences in muscle excitation and oxygenation, but not in force fluctuations or active hyperemia resulting from a fatiguing, bilateral isometric task

It remains to be fully elucidated if there are sex-specific physiological adjustments within the human neuromuscular and vascular systems that contribute to symptoms of fatigue during a sustained bilateral task. This, in part, is likely due to various limitations in experimental design such as an inability to independently record force fluctuations from each limb.Objective. Therefore, the purpose of the current study was to examine the fatigue-induced changes in muscle excitation, force fluctuations, skeletal muscle tissue saturation (StO₂), and muscle blood flow resulting from a sustained, bilateral task.Approach. Thirty healthy, college-aged adults (15 males, 15 females) performed a bilateral leg task at 25% of maximum voluntary isometric (MVIC). Before and after the task, MVICs were completed. Resting and post-task femoral artery blood flow (FABF) were determined. Muscle excitation was quantified as electromyographic amplitude (EMG AMP) from the right and left vastus lateralis. During the task, force fluctuations were determined independently from each leg. The StO₂signal was collected with a near-infrared spectroscopy device attached to the right vastus lateralis. The rate of change in these variables was calculated via simple linear regression. The exercise-induced magnitude of change in MVIC (i.e. performance fatigability) and FABF (i.e. active hyperemia) was determined.Main Results. There was no sex difference in the percent decline in MVIC (20.5 ± 20.1% versus 16.4 ± 3.5%;p> 0.05). There were no inter-leg differences in EMG AMP or force fluctuations. The males exhibited a faster rate of increase in EMG AMP (b= 0.13 versusb= 0.08;p< 0.001), whereas the females exhibited a slower rate of decline in StO₂(b= -0.049 versusb= -0.080). There was no sex difference in force fluctuations or change in FABF.Significance. Males and females likely have different neuromuscular strategies and muscle characteristics, but these did not elicit a sex difference in performance fatigability.

Men Exhibit Greater Pain Pressure Thresholds and Times to Task Failure but Not Performance Fatigability Following Self-Paced Exercise

The purpose of the current study was to determine if, and to what extent, sex differences in performance fatigability after a sustained, bilateral leg extension, anchored to a moderate rating of perceived exertion (RPE), could be attributed to muscle size, muscular strength, or pain pressure threshold (PPT) in young, healthy adults. Thirty adults (men: n = 15, women: n = 15) volunteered to complete a sustained leg extension task anchored to RPE = 5 (10-point OMNI scale) as well as pretest and posttest maximal voluntary isometric contraction (MVIC) trials. The fatigue-induced decline in MVIC force was defined as performance fatigability. We used muscle cross-sectional area (mCSA) to quantify muscle size and a dolorimeter to assess PPT. The sustained task induced fatigue such that both men and women exhibited significant (p < 0.05) decreases in MVIC force from pretest to posttest (M = 113.3, SD =24.2 kg vs. M = 98.3, SD = 23.1 kg and M = 73.1, SD =14.5 kg vs. M = 64.1, SD = 16.2 kg, respectively), with no significant sex differences in performance fatigability (grand M = 12.6, SD =10.6%). Men, however, exhibited significantly (p < 0.05) longer time to task failure (TTF) than women (M = 166.1, SD =83.0 seconds vs. M = 94.6, SD =41.7) as well as greater PPT (M = 5.9, SD = 2.2 kg vs. M = 3.4, SD =1.1 kg). The only significant predictor of performance fatigability was PPT. In conclusion, differences in PPT, at least in part, mediate variations in TTF during self-paced exercise anchored to a specific RPE and resulting in performance fatigability.