Sex comparisons for relative peak torque and electromyographic mean frequency during fatigue

Effects of a thorstensson fatiguing protocol on isometric and isokinetic performance

OBJECTIVE: Having participants perform 50 maximal isokinetic contractions, as introduced by Thorstensson and Karlsson (1976), is to this day one of the most commonly used fatigue protocols. Purpose: To determine to what extent a Thorstensson fatiguing protocol affects isokinetic and isometric performance characteristics. METHODS: Twenty-five college-aged men performed an isokinetic fatigue protocol consisting of 50 maximal elbow flexions at a moderate speed (180∘⋅s-1). Pre- and post-tests were used to calculate fatigue indices (FI%) for the following variables: isometric and isokinetic peak torque (PT), isometric rate of torque development (RTD), and maximum acceleration (ACCmax). RESULTS: Each of the four dependent variables significantly decreased with fatigue (each demonstrated p< 0.001), but not of the same magnitude. Isometric PT FI (-18.7%) was significantly less than isokinetic PT FI (-45.1%, p⩽ 0.001) and ACCmax FI (-26.3%) was significantly less than isometric RTD FI (-54.9%, p⩽ 0.001). There was a significant positive relationship between isometric and isokinetic PT FI% (r= 0.60, p< 0.002) as well as between isometric PT FI% and RTD FI% (r= 0.40, p< 0.046). There was no significant relationship observed between RTD FI% and ACCmax FI% nor between isokinetic PT FI% and ACCmax FI%. CONCLUSIONS: This investigation observed different patterns of response in maximal strength between isometric and isokinetic assessments following a isokinetic fatigue protocol. Additionally, the ability to rapidly generate strength and velocity had significantly different responses to fatigue between isometric and dynamic assessments. Due to these different responses, we recommend that assessments of fatigue at least include the same testing modality as the modality of the fatigue protocol.

Sex differences in muscle fatigue following isokinetic muscle contractions

Muscle fatigue is a limiting factor of human performance. It is unclear whether sex-based differences in fatigability exist during dynamic exercise of varying velocities of contraction. We aimed at exploring sex differences in muscle fatigue elicited by maximal isokinetic muscle contractions performed at different angular velocities. Twenty-six healthy participants (13 men: 23.2 ± 1.5; 13 women: 21.9 ± 3.0 years) were tested for concentric knee-extension at slow, moderate and fast angular isokinetic velocity (60, 180 and 300º.s^-1, respectively), on non-consecutive days. The impact of sex on fatigue resistance and consecutive recovery for each isokinetic condition was explored by calculating the percent change in maximal voluntary isometric contraction (MVIC) and in rate of torque development (RTD), from pre- to post-isokinetic exercise (30 repetitions). The isokinetic fatigue index was also determined. No sex differences were obtained in response to isokinetic contractions completed at 60º.s^-1. After performing muscle contractions at 300º.s^-1, women had a significantly greater loss in MVIC than men (- 18.4 ± 5.5 vs. - 12.9 ± 3.8%; p = 0.009) and larger decreases in work output during isokinetic exercise (- 34.2 ± 8.9 vs - 27.5 ± 10.6%; p = 0.017). Recovery of initial MVIC strength was greater for women post-exercise at 180º.s^-1 (15.6 ± 4.1% vs. 6.7 ± 9.5; p = 0.003). No differences were found between sexes in any condition for RTD from pre- to post-fatigue. These results suggest the presence of a sexually dimorphic fatigability in response to dynamic (isokinetic) contractions favouring men at higher absolute velocities of contraction.

Myosin heavy chain expression relationships to power-load and velocity-load curves

BACKGROUND

Velocity- and power-based training are popular methods of determining training session loads and volumes. One factor that may influence load-velocity and load-power properties of an individual is the myosin heavy chain (MHC) composition of the muscle. The aim of this study was to examine the relationship between MHC composition and both load-velocity and load-power properties of muscle performance.

METHODS

Forty-two men with a variety of training backgrounds took part in this study (mean±SD; age=22.4±3.5 yrs, hgt=1.78±0.07 m, BW=78.7±13.3 kg). After testing leg extension one repetition maximum (1 RM), subjects performed maximal effort leg extensions at loads from 30% to 90% 1 RM. Muscle biopsies from the vastus lateralis were analyzed via SDS-PAGE electrophoresis technique for MHC content (IIx=13.8±12.9%, IIa=49.4±10.3%, I=36.8±11.3%). Leg extension rotational velocity and power were plotted against relative loads for all subjects.

RESULTS

Significant correlations (P<0.05) were observed for MHC IIa with all performance variables (i.e. slopes, intercepts, peaks and relative loads). Relationships indicated that greater %MHC IIa was associated with greater velocity intercepts, more negative load-velocity slopes, greater maximal power, and with maximal power occurring at a lower relative intensity (% 1 RM).

CONCLUSIONS

These data indicate that muscle velocity and power characteristics appear to be partially influenced by MHC content in a manner consistent with single muscle fiber contractile properties.

Intrarater reliability and agreement of a modified Closed Kinetic Chain Upper Extremity Stability Test

OBJECTIVES

To assess the reliability of a modified procedure for Closed Kinetic Chain Upper Extremity Stability Test (CKCUEST).

DESIGN

Intra- and intersession reliability and agreement; SETTING: Clinical.

PARTICIPANTS

Twenty-seven asymptomatic athletes.

MAIN OUTCOME MEASURES

The modifications (m-CKCUEST) in CKCUEST procedure consisted in hand spacing at one half arm-span, and to complete the three regular-series of 15 s exertion by performing a fourth 1-min series during which the number of touches was counted every 15 s. The intra- and intersession reliability and agreement were assessed for the numbers of touches in order to produce two outcome measures: m-CKCUEST score and muscular endurance index.

RESULTS

The most reliable m-CKCUEST score was obtained when averaging the numbers of touches of the second and third sets (Intraclass Coefficient of Correlation(3,k); ICC = 0.92). Good reliability was found for muscular endurance index computed when dividing the one-half number of touches counted during the last 30 s of 1-min set, by the m-CKCUEST score calculated above (ICC = 0.86).

CONCLUSIONS

The m-CKCUEST allowed the production of two reliable outcome measures, which assessed the upper limb stability and the muscular endurance. Such outcomes may be used in a follow-up to assess performance or rehabilitation level.

Altered sarco(endo)plasmic reticulum calcium adenosine triphosphatase 2a content: Targets for heart failure therapy

Sarco(endo)plasmic reticulum calcium adenosine triphosphatase is responsible for transporting cytosolic calcium into the sarcoplasmic reticulum and endoplasmic reticulum to maintain calcium homeostasis. Sarco(endo)plasmic reticulum calcium adenosine triphosphatase is the dominant isoform expressed in cardiac tissue, which is regulated by endogenous protein inhibitors, post-translational modifications, hormones as well as microRNAs. Dysfunction of sarco(endo)plasmic reticulum calcium adenosine triphosphatase is associated with heart failure, which makes sarco(endo)plasmic reticulum calcium adenosine triphosphatase a promising target for heart failure therapy. This review summarizes current approaches to ameliorate sarco(endo)plasmic reticulum calcium adenosine triphosphatase function and focuses on phospholamban, an endogenous inhibitor of sarco(endo)plasmic reticulum calcium adenosine triphosphatase, pharmacological tools and gene therapies.

The improvement of suspension training for trunk muscle power in Sanda athletes

The aim of this study was to investigate whether both suspension training (ST) and traditional training (TT) can improve Sanda athlete's strength quality of trunk muscles and to explore the effect of suspension training on Sanda athletes' trunk muscle power production. Twelve elite Sanda athletes from the Competitive Sports School of Shanghai University of Sport were randomly assigned to experimental group (EG) and control group (CG). EG and CG were regularly trained with suspension training and traditional strength training for 40 minutes three times per week. The total duration of training was 10 weeks. The measurements including peak torque (PT), PT/body weight (BW), and rate of force development (RFD) were used to assess trunk muscles strength. The results showed that there were significant differences between the two groups' performance when it was tested at the higher velocity of dynamometer (test of muscle power), but less significant differences when the two groups performance was tested at the lower velocity of dynamometer (test of maximum strength). The conclusion of this study is that compared with traditional training methods, suspension training can improve back and trunk flexion muscles strength more effectively. In particular, suspension training can improve the explosive power of trunk extension and flexion muscles.

Influence of gender on muscle fatigue during dynamic knee contractions

PURPOSE

The purpose was to compare quadriceps muscle fatigue and change in surface electromyogram (sEMG) spectral power, muscle thickness, and peak torque (normalized by body weight) in men and women during isokinetic knee contractions.

METHODS

Nineteen healthy volunteers (10 men, 9 women) participated. The volunteers performed 32 consecutive maximal isokinetic knee contractions for peak torque and muscle fatigue index (FI). The sEMG data were analyzed using wavelet analysis for median frequency (MF). Muscle thickness was measured using ultrasonography.

RESULTS

Men had a significantly higher FI, peak torque (Nm/kg), muscle thickness than women (p<0.05). A significant linear decreased MF slope in the vastus lateralis was observed (p<0.05) in men than in women. There was no significant difference in MF slope in the vastus medialis between men and women.

CONCLUSION

During muscle fatigue assessment, men had a significantly greater muscle thickness, knee extension peak torque, and a higher decrease of MF slope than women. Our results indicate that specific muscle fatigue observed during repeated muscle knee contractions is significantly influence by gender and affects MF slope, knee extension peak torque, and muscle thickness.

Influence of Hamstring Fatigue on the Estimated Percentage of Fast-Twitch Muscle Fibers for the Vastus Lateralis

A previous study has demonstrated the ability to roughly estimate the percentage of fast-twitch muscle fibers for the vastus lateralis through the analysis of peak torque values during fatiguing isokinetic testing. We examined whether use of the hamstrings influenced peak torque and electromyographic (EMG) responses for the quadriceps during fatiguing isokinetic muscle actions. On 2 separate occasions, 21 men (mean age = 23 years) performed 50 repeated, maximal concentric isokinetic muscle actions of the left leg extensors at a velocity of 180°·s. For 1 trial, the subjects maximally flexed the knee joint after each full extension to bring the dynamometer's lever arm back to the starting position. For the other trial, the subjects relaxed after each maximal extension and an investigator assisted in returning the lever arm. Surface EMG signals were detected from the vastus lateralis and biceps femoris throughout testing. Dependent variables that assessed the decline in peak torque and EMG mean frequency for the vastus lateralis were examined using dependent samples t-tests, effect size statistics, and the number of subjects who exceeded the minimal difference needed to be considered real. Our results showed small mean differences between the trials (Cohen's d ≤0.136). For the estimated percentage of fast-twitch fibers, none of the subjects showed a difference between trials that we considered meaningful. The mean estimated percentages of fast-twitch fibers were 61.6 and 60.1. Collectively, use of the hamstrings during fatiguing isokinetic testing of the quadriceps had little influence on peak torque and EMG.

Improved Data Reporting in RQES: from volumes 49, 59, to 84

This commentary provides a review of changes in data reporting in Research Quarterly for Exercise and Sport from Volumes 49 and 59 to 84. Improvements were noted in that all articles reported means, standard deviations, and sample sizes, while most (87%) articles reported an estimate of effect size (ES). Additional reporting recommendations were made about ES for mean differences, use of appropriate estimates of variability, when to use a table or figure, use of multivariate analyses, and power analyses.

The effects of poliomyelitis on motor unit behavior during repetitive muscle actions: a case report

Background

Acute paralytic poliomyelitis is caused by the poliovirus and usually results in muscle atrophy and weakness occurring in the lower limbs. Indwelling electromyography has been used frequently to investigate the denervation and innervation characteristics of the affected muscle. Recently developed technology allows the decomposition of the raw surface electromyography signals into the firing instances of single motor units. There is limited information regarding this electromyographic decomposition in clinical populations. In addition, regardless of electromyographic methods, no study has examined muscle activation parameters during repetitive muscle actions in polio patients. Therefore, the purpose of this study was to examine the motor unit firing rates and electromyographic amplitude and center frequency of the vastus lateralis during 20 repetitive isometric muscle actions at 50% maximal voluntary contraction in healthy subjects and one patient that acquired acute paralytic poliomyelitis.

Case presentation

One participant that acquired acute type III spinal poliomyelitis (Caucasian male, age = 29 yrs) at 3 months of age and three healthy participants (Caucasian females, age = 19.7 ± 2.1 yrs) participated in this study. The polio participant reported neuromuscular deficiencies as a result of disease in the hips, knees, buttocks, thighs, and lower legs. None of the healthy participants reported any current or ongoing neuromuscular diseases or musculoskeletal injuries.

Conclusion

An acute bout of poliomyelitis altered motor unit behavior, such as, healthy participants displayed greater firing rates than the polio patient. The reduction in motor unit firing rates was likely a fatigue protecting mechanism since denervation via poliomyelitis results in a reduction of motorneurons. In addition, the concurrent changes in motor unit firing rates, electromyography amplitude and frequency for the polio participant would suggest that the entire motorneuron pool was utilized in each contraction unlike for the healthy participants. Finally, healthy participants exhibited changes in all electromyographic parameters during the repetitive muscle actions despite successfully completing all contractions with only a slight reduction in force. Thus, caution is warranted when quantifying muscular fatigue via motor unit firing rates and other electromyographic parameters since the parameters changed despite successful completing of all contractions with only a moderate reduction in strength in healthy subjects.

QUADRICEPS STRENGTH, KNEE PAIN AND FUNCTIONAL PERFORMANCE WITH PATELLAR TAPING IN KNEE OSTEOARTHRITIS

Background: Patellar taping has long been reported to be effective in relieving pain in patients with patello-femoral pain syndrome (PFPS). Yet, there is lack of knowledge that supports its use in knee osteoarthritis (OA) management. Purpose: This study examined the effect of therapeutic patellar taping on concentric and eccentric quadriceps muscle peak torques, VAS pain scores, 6-minute walking distance and stair climbing time in patients with knee OA. Methods: A total of 30 female patients with symptomatic knee OA with mean age 51.8 ± 6.3 years and BMI 32.56 ± 3.26 m2/kg participated in the study. They were tested under three taping conditions that were tested randomly; therapeutic, placebo and no-tape. Results: Repeated measure MANOVA revealed that the quadriceps muscle peak torques and 6-minute walking distance increased significantly (p < 0.05) and the VAS scores and stair climbing time decreased significantly with therapeutic tape use compared with the other two tapes. Moreover, the quadriceps muscle peak torques increased significantly and the VAS scores decreased significantly with placebo tape use compared with no-tape use, with no significant difference (p > 0.05) in between for the 6-minute walking distance and stair climbing time. Conclusion: The findings indicate that therapeutic patellar taping is effective in improving quadriceps strength and functional performance and reducing pain in patients with knee OA.