Log-Transformed Electromyography Amplitude-Power Output Relationship: Single-Leg Knee-Extensor Versus Single-Leg Cycle Ergometry

Exploring lower limb muscle activity and performance variations during instrumented Sit-to-Stand-to-Sit in sedentary individuals: Influence of limb dominance and testing modalities

PURPOSE

to explore lower limb muscle activity concerning limb dominance, as well as variations in force and power during the standing up and sitting down phases of the instrumented sit-to-stand-to-sit test in sedentary individuals, across isokinetic and isotonic modalities.

METHODS

33 sedentary individuals underwent testing using a functional electromechanical dynamometer in both isokinetic and isotonic modes, accompanied by surface electromyography.

RESULTS

In the isokinetic mode, the non-dominant gastrocnemius medialis and vastus medialis exhibited significantly (p < 0.05) higher muscle activity values during the standing up and sitting down phase compared to dominant counterparts. In the isotonic mode standing up phase, significant differences in muscle activity were noted for non-dominant gastrocnemius medialis, vastus medialis, and biceps femoris compared to their dominant counterparts. The sitting down phase in isotonic mode showed higher muscle activity for non-dominant vastus medialis compared to dominant vastus medialis. Regard to performance outcomes, significantly lower (p < 0.0001) values were observed for standing up (12.7 ± 5.1 N/kg) compared to sitting down (15.9 ± 6.1 N/kg) peak force, as well as for standing up (18.7 ± 7.8 W/kg) compared to sitting down (25.9 ± 9.7 W/kg) peak power in isokinetic mode. In isotonic mode, lower values were found for sitting down (6.5 (6.3-7.1) N/kg) compared to standing up (7.8 (7.3-8.9) N/kg) peak force and for sitting down (18.5 (13.2-21.7) W/kg) compared to standing up (33.7 (22.8-41.6) W/kg) peak power.

CONCLUSIONS

Limb dominance influences lower-limb muscle activity during the instrumented sit-to-stand-to-sit test, and the choice of testing mode (isokinetic or isotonic) affects muscle engagement and performance outcomes.

Caffeine Expectancy Does Not Influence the Physical Working Capacity at the Fatigue Threshold

ABSTRACT

Ambrozy, CA, Hawes, NE, Hayden, OL, Sortzi, I, and Malek, MH. Caffeine expectancy does not influence the physical working capacity at the fatigue threshold. J Strength Cond Res 38(6): 1056-1062, 2024-The placebo effect occurs when a desired outcome is experienced due to the belief that a treatment is effective, even in the absence of an active ingredient. One explanation for this effect is based on a person's expectations of a drug or supplement. Although caffeine's effects on sports performance have been studied, little is known about how expectations of caffeine affect neuromuscular fatigue during continuous muscle action. The physical working capacity at the fatigue threshold (PWCFT) can be used to assess neuromuscular fatigue noninvasively using surface electromyography. Thus, the purpose of this study was to investigate whether caffeine expectancy influences PWCFT. We hypothesized that regardless of expectancy, caffeine consumption would delay neuromuscular fatigue. The study involved 8 healthy college-aged men (mean ± SEM: age, 25.6 ± 1.0 years) who visited the laboratory on 4 occasions, each separated by 7 days. The subjects completed 4 experimental conditions, in random order, where they were told that they were consuming caffeine or placebo and either received caffeine or placebo. After consuming the drink, the subjects remained in the laboratory for an hour and then performed an incremental exercise test. The results showed that the condition where subjects were told that they were consuming caffeine and received caffeine had significantly higher mean values for maximal power output (F(3, 21) = 11.75; p < 0.001), PWCFT (F(3, 21) = 12.28; p < 0.001), PWCFT (%maximal power output; F(3, 21) = 8.75; p < 0.001), and heart rate at end exercise (%predicted; F(3, 21) = 3.83; p = 0.025) compared with the 2 conditions where placebo was received. However, no statistically significant mean differences were found from the condition where subjects were told that they were consuming placebo but consuming caffeine. This suggests that a person's expectancy and potential somatic response may serve as a cue for how an ergogenic aid or placebo could affect subsequent performance.

The Influence of Cold Therapy on the Physical Working Capacity at the Electromyographic Threshold for Consecutive Exercise Sessions

BACKGROUND

The purpose of this study was to determine whether cold therapy after the first exercise test influences the physical working capacity at the fatigue threshold (PWCFT) during the second exercise test. We hypothesized that cold therapy would delay the onset of PWCFT for the second exercise test relative to the control visit (i.e., no cold therapy).

METHODS

Eight healthy college-aged men volunteered for the present study. For each of the two visits, subjects performed incremental, single-leg, knee-extensor ergometer, followed by either resting for 30 min (control visit) or having a cold pack applied for 15 min and then resting for 15 min (experimental visit). Then, the same exercise test was performed. The order of visits (control vs. experimental) was randomized for each subject. The exercise indices and PWCFT were determined for each of the two visits and statistically analyzed using two-way repeated measures analysis of variance.

RESULTS

The results indicate no significant (p > 0.05) mean differences for maximal power output, heart rate at end-exercise, and PWCFT between the control and cold therapy visits. Moreover, there were no significant (p > 0.05) mean differences between the first and second exercise workbout within each visit.

CONCLUSIONS

The findings of this study suggest that cold therapy did not influence neuromuscular fatigue.

Acceleration Profiles and the Isoinertial Squatting Exercise: Is There a Direct Effect on Concentric-Eccentric Force, Power, and Neuromuscular Efficiency?

OBJECTIVE

To examine the selective influences of distinct acceleration profiles on the neuromuscular efficiency, force, and power during concentric and eccentric phases of isoinertial squatting exercise.

DESIGN

Cross-sectional study.

SETTING

Biomechanics laboratory of the university.

PARTICIPANTS

A total of 38 active adults were divided according to their acceleration profiles: higher (n = 17; >2.5 m/s2) and lower acceleration group (n = 21; <2.5 m/s2).

INTERVENTION

All subjects performed squats until failure attached to an isoinertial conic pulley device monitored by surface electromyography of rectus femoris, vastus medialis, vastus lateralis, biceps femoris, and semitendinosus.

MAIN OUTCOME MEASURES

An incremental optical encoder was used to assess maximal and mean power and force during concentric and eccentric phases. The neuromuscular efficiency was calculated using the mean force and the electromyographic linear envelope.

RESULTS

Between-group differences were observed for the maximal and mean force (Prange = .001-.005), power (P = .001), and neuromuscular efficiency (Prange = .001-.03) with higher significant values for the higher acceleration group in both concentric and eccentric phases.

CONCLUSION

Distinct acceleration profiles affect the neuromuscular efficiency, force, and power during concentric and eccentric phases of isoinertial squatting exercise. To ensure immediate higher levels of power and force output without depriving the neuromuscular system, acceleration profiles higher than 2.5 m/s2 are preferable. The acceleration profiles could be an alternative to evolve the isoinertial exercise.

The Evolution of the Physical Work Capacity at the Fatigue Threshold Test: Past, Present, and Future

ABSTRACT

Feldpausch, JE, Blok, AL, Frederick, EL, Coburn, JW, and Malek, MH. The evolution of the physical work capacity at the fatigue threshold test: past, present, and future. J Strength Cond Res 35(12): 3529-3536, 2021-The assessment of neuromuscular fatigue using surface electromyography has evolved over the past 40 years while maintaining some of the original key features. In this mini-review article, the goal will be to briefly present a history and systems of the physical working capacity at the fatigue threshold (PWCFT). In addition, we will discuss studies that have investigated the effect of different interventions such as supplementation, exercise, and cognitive fatigue to examine what stimuli influence the PWCFT. The latter section of this mini-review will discuss future studies that may provide additional information related to the underlying physiological mechanism(s) that influences the PWCFT. We will conclude with the practical application of PWCFT in health and sports settings.

Comparisons of Resistance Training and "Cardio" Exercise Modalities as Countermeasures to Microgravity-Induced Physical Deconditioning: New Perspectives and Lessons Learned From Terrestrial Studies

Prolonged periods in microgravity (μG) environments result in deconditioning of numerous physiological systems, particularly muscle at molecular, single fiber, and whole muscle levels. This deconditioning leads to loss of strength and cardiorespiratory fitness. Loading muscle produces mechanical tension with resultant mechanotransduction initiating molecular signaling that stimulates adaptations in muscle. Exercise can reverse deconditioning resultant from phases of detraining, de-loading, or immobilization. On Earth, applications of loading using exercise models are common, as well as in μG settings as countermeasures to deconditioning. The primary modalities include, but are not limited to, aerobic training (or "cardio") and resistance training, and have historically been dichotomized; the former primarily thought to improve cardiorespiratory fitness, and the latter primarily improving strength and muscle size. However, recent work questions this dichotomy, suggesting adaptations to loading through exercise are affected by intensity of effort independent of modality. Furthermore, similar adaptations may occur where sufficient intensity of effort is used. Traditional countermeasures for μG-induced deconditioning have focused upon engineering-based solutions to enable application of traditional models of exercise. Yet, contemporary developments in understanding of the applications, and subsequent adaptations, to exercise induced muscular loading in terrestrial settings have advanced such in recent years that it may be appropriate to revisit the evidence to inform how exercise can used in μG. With the planned decommissioning of the International Space Station as early as 2024 and future goals of manned moon and Mars missions, efficiency of resources must be prioritized. Engineering-based solutions to apply exercise modalities inevitably present issues relating to devices mass, size, energy use, heat production, and ultimately cost. It is necessary to identify exercise countermeasures to combat deconditioning while limiting these issues. As such, this brief narrative review considers recent developments in our understanding of skeletal muscle adaptation to loading through exercise from studies conducted in terrestrial settings, and their applications in μG environments. We consider the role of intensity of effort, comparisons of exercise modalities, the need for concurrent exercise approaches, and other issues often not considered in terrestrial exercise studies but are of concern in μG environments (i.e., O2 consumption, CO2 production, and energy costs of exercise).

Similar acute physiological responses from effort and duration matched leg press and recumbent cycling tasks

The present study examined the effects of exercise utilising traditional resistance training (leg press) or ‘cardio’ exercise (recumbent cycle ergometry) modalities upon acute physiological responses. Nine healthy males underwent a within session randomised crossover design where they completed both the leg press and recumbent cycle ergometer conditions. Conditions were approximately matched for effort and duration (leg press: 4 × 12RM using a 2 s concentric and 3 s eccentric repetition duration controlled with a metronome, thus each set lasted  60 s; recumbent cycle ergometer: 4 × 60 s bouts using a resistance level permitting 80–100 rpm but culminating with being unable to sustain the minimum cadence for the final 5–10 s). Measurements included VO₂, respiratory exchange ratio (RER), blood lactate, energy expenditure, muscle swelling, and electromyography. Perceived effort was similar between conditions and thus both were well matched with respect to effort. There were no significant effects by ‘condition’ in any of the physiological responses examined (all p > 0.05). The present study shows that, when both effort and duration are matched, resistance training (leg press) and ‘cardio’ exercise (recumbent cycle ergometry) may produce largely similar responses in VO₂, RER, blood lactate, energy expenditure, muscle swelling, and electromyography. It therefore seems reasonable to suggest that both may offer a similar stimulus to produce chronic physiological adaptations in outcomes such as cardiorespiratory fitness, strength, and hypertrophy. Future work should look to both replicate the study conducted here with respect to the same, and additional physiological measures, and rigorously test the comparative efficacy of effort and duration matched exercise of differing modalities with respect to chronic improvements in physiological fitness.