Maximal Isometric Elbow Flexion Research Articles

The Impact Of Increasing Blood Flow Restriction Pressure During Already Occlusive Contractions.

Restricting blood flow during resistance exercise reduces the number of repetitions required to see adaptations, with higher blood flow restriction pressures resulting in greater muscle fatigue when sub-occlusive pressures are applied. The augmented fatigue is thought to be related to alterations in blood flow, but the impact of increasing the restriction pressure during completely occlusive contractions remains unknown and may provide information on alternative mechanisms responsible for fatigue. PURPOSE: To determine whether increasing the blood flow restriction pressure reduces local muscular endurance and increases discomfort when the contractions are already occlusive. We also the examined potential changes in force steadiness. METHODS: Twenty-two individuals performed a contraction at 30% of maximal isometric elbow flexion force for as long as possible. One arm completed the contraction with 100% of arterial occlusion pressure applied, while the other arm had 150% of arterial occlusion pressure applied. At the end of the protocol individuals were asked to rate their perceived discomfort. A Bayesian paired samples t-test was used to compare differences in time to task failure, average force output, and force steadiness and a Wilcoxon signed rank test was performed to compare differences in discomfort between high and low pressure conditions. RESULTS: Individuals had a longer time to task failure when performing the 100% arterial occlusion condition as compared to the 150% arterial occlusion pressure condition (time to task failure = 82.4 vs. 70.8 seconds; BF10 = 5.77). There were no differences in discomfort between the 100% and 150% conditions (median discomfort = 5.5 vs. 6; p = 0.243) nor were there differences in force steadiness (standard deviation of force output 1.09 vs. 1.06 %; BF10 = 0.29). CONCLUSIONS: The results of the present study suggest that, even when contractions are already occlusive, increasing the restriction pressure reduces local muscle endurance but does not impact discomfort or force steadiness. This provides an indication that mechanisms other than the direct alteration of blood flow are contributing to the increased fatigue with added restrictive pressure. Future studies are needed to examine neural mechanisms that may explain this finding.

Effect of Anodal Transcranial Direct Current Stimulation of the Motor Cortex on Elbow Flexor Muscle Strength in the Very Old.

Muscle weakness predisposes older adults to a fourfold increase in functional limitations and has previously been associated with reduced motor cortex excitability in aging adults. The purpose of this study was to determine whether a single session of anodal transcranial direct current stimulation (tDCS) of the motor cortex would increase elbow flexion muscle strength and electromyographic (EMG) amplitude in very old individuals. Eleven very old individuals-85.8 (4.3) years-performed 3 maximal isometric elbow flexion contractions before and after 20 minutes of sham or anodal tDCS on different days. Order of stimulation was randomized, and the study participants and investigators were blinded to condition. In addition, voluntary activation capacity of the elbow flexors was determined by comparing voluntary and electrically evoked forces. Anodal tDCS did not alter muscle strength or EMG activity in comparison to sham stimulation. Elbow flexion voluntary activation capacity was very high among the study participants: 99.3% (1.8%). Contrary to our hypothesis, we observed no effect of anodal tDCS and no impairment in elbow flexor voluntary activation capacity in the very old. Whether anodal tDCS would exert a positive effect and support our initial hypothesis in another muscle group that does exhibit impairments in voluntary activation in older adults is a question that is still to be addressed.

Spike shape analysis for the surface and needle electromyographic interference pattern

The ability of surface and needle electromyographic (EMG) spike shape measures to match changes in motor unit recruitment, firing rate, and synchronization during force gradation, were compared. The purpose of the study was to determine the force level at which the surface EMG spike shape measures no longer parallel their indwelling analogues. Secondarily, the impact of the noise rejection criterion on the sensitivity of the spike shape measures was examined. Maximal isometric elbow flexion ramp contractions were performed while recording surface and needle EMG from the biceps brachii. Spike shape measures were calculated in 500 ms epochs over the duration of the ramp contraction. The spike threshold for needle EMG spike detection was varied to examine the effect of the algorithm’s selectivity. The pattern of change across force levels between surface and needle EMG measures was compared. Spike detection resulted in the same pattern of change for both surface and needle amplitude measures over the gradation of force. Frequency measures and mean number of peaks per spike (MNPPS) were affected by electrode-source distance and spike threshold. Surface and needle frequency measures changed in parallel to 50% MVC while the MNPPS plateaued at 50–55% MVC. Spike shape analysis of surface EMG can track changes in the interference pattern produced by recruitment and rate-coding up to 50% MVC.

Effects of mate tea consumption on muscle strength and oxidative stress markers after eccentric exercise

Dietary phytochemical supplementation may improve muscle recovery from exercise. In this study, we investigated the effect of mate tea (MT) consumption - a phenol-rich beverage - on muscle strength and oxidative stress biomarkers after eccentric exercise. In a randomised, cross-over design, twelve men were assigned to drink either MT or water (control; CON) for 11 d. On the 8th day, subjects performed three sets of twenty maximal eccentric elbow flexion exercises. Maximal isometric elbow flexion force was measured before and at 0, 24, 48 and 72 h after exercise. Blood samples were obtained before and at 24, 48 and 72 h after exercise and analysed for total phenolics, GSH, GSSG, GSH:GSSG ratio and lipid hydroperoxides (LOOH). After eccentric exercise, muscle strength was significantly reduced over time, regardless of treatments. However, MT improved the rate of strength recovery by 8·6 % on the 1st day after exercise (P<0·05). Plasma concentration of total phenolic compounds was higher in MT than in CON at all time points (P<0·05) but decreased significantly at 72 h after exercise in both trials (P<0·05). Blood levels of GSH were significantly decreased at 48 and 72 h after exercise in CON (P<0·05) but did not change over time in MT. No significant changes were observed for GSSG, GSH:GSSG ratio and LOOH levels. MT intake did not influence muscle strength at all time points assessed but hastened the strength recovery over 24 h after exercise. MT also favoured the concentration of blood antioxidant compounds.

Impact of stretched position of a shortened muscle on active command in spastic paresis

In spastic paresis, factors limiting active movement include antagonist contracture, agonist paresis, and spastic cocontraction. We studied agonist and antagonist muscle activation around the elbow to determine the role of the degree of muscle stretch in modifying paresis and cocontraction. Eighteen healthy (age 47 ± 10) and 15 hemiparetic (age 42 ± 16) subjects performed maximal isometric elbow flexion and extension 5-second efforts, with elbow flexed and extended. Using biceps and triceps brachii surface electromyography, we determined for each muscle: (i) the Mean Rectified Voltage (MRV) during the 500 ms peak voluntary agonist recruitment elbow flexed (MRV ago500F ) and elbow extended (MRV ago500E ); (ii) the coefficient of stretch-sensitivity (CSS) of agonist recruitment, calculated as (MRV ago500F -MRV ago500E )/MRV ago500F ; (iii) the cocontraction index (CCI) in each elbow position, ratio of the MRV from each muscle during an opposite movement, MRV antago5 to MRV ago500 . We compared the dominant arm in healthy subjects with the non-paretic and paretic arms in hemiparetic subjects. X V1 was 175 ± 11° in the elbow flexors (maximal passive elbow extension; coefficient of shortening, 2.7%) and 163 ± 7° in the elbow extensors (no shortening) . CSS was not significantly different from 0 in the healthy and non-paretic arm; however, CSS in the paretic arm was −21 ± 10% in the paretic elbow extensors vs −4 ± 7% in the non-paretic arm ( P vs extended, P = 0.013). Triceps brachii CCI with the elbow flexed was 0.10 ± 0.05 [95%CI, 0.03–0.17], 0.15 ± 0.10 [0.07–0.23] and 0.26 ± 0.24 [0.18–0.34], in the healthy, non-paretic and paretic arm respectively (between-group difference P = 0.011), and 0.12 ± 0.06 [95%CI, 0.03–0.21], 0.15 ± 0.08 [0.06–0.25], and 0.38 ± 0.32 [0.28–0.48] with the elbow extended (between-group difference P vs extended, NS). In hemiparesis, elbow extended position deteriorates active command at both agonist and antagonist levels: decreasing voluntary recruitment of agonist MNs–a phenomenon defined as stretch-sensitive paresis–and increasing antagonist co-contraction. This may occur through physiological effects of high-threshold afferent fiber recruitment in contractured elbow flexors.

Sex-related differences in maximal rate of isometric torque development

Sex-differences in the maximum rate of torque development (dτ/dtmax) may be due to differences in maximum muscle strength, because higher torque values mathematically lead to higher values for the rate of change in torque. The rate of change in the isometric torque-time curve is often normalized to the isometric maximum voluntary contraction (MVC) to evaluate males and females on a relative scale. Normalization eliminates sex-differences in dτ/dtmax in the lower limbs because males and females are more comparable (i.e., differences between the sexes are relatively small) with respect to both muscle size and strength. However, normalization fails to result in parody in dτ/dtmax of the upper limb, leading to the idea that other factors may be involved. This study determined if sex-differences in dτ/dtmax in the upper limb can be attributed to differences in isometric MVC and/or a neural variable related to rate of increase in muscle activation (Q30). Forty-six participants (23 males, 23 females) performed maximal isometric elbow flexion contractions, “as hard and as fast as possible”. Maximum torque (τmax), dτ/dtmax, and the rate of increase in surface electromyographic (sEMG) activity (Q30) were assessed. Muscle plus bone cross-sectional area (M+B CSA) of the upper arm was calculated to estimate differences in muscle size, only for comparative purposes. Maximum strength (55.5%) and muscle size (41.9%) of the elbow flexors in males were much greater than that of females (p<0.05). There was a large difference (61.2%) between males and females with respect to dτ/dtmax that was reduced by statistical correction using an analysis of covariance (ANCOVA). The percent differences were reduced to 36.7% (p<0.05) for τmax and 54.4% (p<0.05) for Q30, but was nearly eliminated to 13.8% (p>0.05) when both variables were used simultaneously as covariates. Since sex-differences in the upper limb dτ/dtmax persist, additional neural or biomechanical factors may be involved.

The Effect of Pomegranate Juice Supplementation on Strength and Soreness after Eccentric Exercise

The purpose of this study was to determine if pomegranate juice supplementation improved the recovery of skeletal muscle strength after eccentric exercise in subjects who routinely performed resistance training. Resistance trained men (n = 17) were randomized into a crossover design with either pomegranate juice or placebo. To produce delayed onset muscle soreness, the subjects performed 3 sets of 20 unilateral eccentric elbow flexion and 6 sets of 10 unilateral eccentric knee extension exercises. Maximal isometric elbow flexion and knee extension strength and muscle soreness measurements were made at baseline and 2, 24, 48, 72, 96, and 168 hours postexercise. Elbow flexion strength was significantly higher during the 2- to 168-hour period postexercise with pomegranate juice compared with that of placebo (main treatment effect; p = 0.031). Elbow flexor muscle soreness was also significantly reduced with pomegranate juice compared with that of placebo (main treatment effect; p = 0.006) and at 48 and 72 hours postexercise (p = 0.003 and p = 0.038, respectively). Isometric strength and muscle soreness in the knee extensors were not significantly different with pomegranate juice compared with those using placebo. Supplementation with pomegranate juice attenuates weakness and reduces soreness of the elbow flexor but not of knee extensor muscles. These results indicate a mild, acute ergogenic effect of pomegranate juice in the elbow flexor muscles of resistance trained individuals after eccentric exercise.

Effects of cross-education on the muscle after a period of unilateral limb immobilization using a shoulder sling and swathe

The purpose of this study was to apply cross-education during 4 wk of unilateral limb immobilization using a shoulder sling and swathe to investigate the effects on muscle strength, muscle size, and muscle activation. Twenty-five right-handed participants were assigned to one of three groups as follows: the Immob + Train group wore a sling and swathe and strength trained (n = 8), the Immob group wore a sling and swathe and did not strength train (n = 8), and the Control group received no treatment (n = 9). Immobilization was applied to the nondominant (left) arm. Strength training consisted of maximal isometric elbow flexion and extension of the dominant (right) arm 3 days/wk. Torque (dynamometer), muscle thickness (ultrasound), maximal voluntary activation (interpolated twitch), and electromyography (EMG) were measured. The change in right biceps and triceps brachii muscle thickness [7.0 ± 1.9 and 7.1 ± 2.2% (SE), respectively] was greater for Immob + Train than Immob (0.4 ± 1.2 and -1.9 ± 1.7%) and Control (0.8 ± 0.5 and 0.0 ± 1.1%, P < 0.05). Left biceps and triceps brachii muscle thickness for Immob + Train (2.2 ± 0.7 and 3.4 ± 2.1%, respectively) was significantly different from Immob (-2.8 ± 1.1 and -5.2 ± 2.7%, respectively, P < 0.05). Right elbow flexion strength for Immob + Train (18.9 ± 5.5%) was significantly different from Immob (-1.6 ± 4.0%, P < 0.05). Right and left elbow extension strength for Immob + Train (68.1 ± 25.9 and 32.2 ± 9.0%, respectively) was significantly different from the respective limb of Immob (1.3 ± 7.7 and -6.1 ± 7.8%) and Control (4.7 ± 4.7 and -0.2 ± 4.5%, P < 0.05). Immobilization in a sling and swathe decreased strength and muscle size but had no effect on maximal voluntary activation or EMG. The cross-education effect on the immobilized limb was greater after elbow extension training. This study suggests that strength training the nonimmobilized limb benefits the immobilized limb for muscle size and strength.

Relationships between surface EMG variables and motor unit firing rates

Although surface electromyography (sEMG) is a widely used electrophysiological technique, its physiological interpretation remains somewhat controversial. This study examined the relationship between motor unit firing rates (MUFR) and the root mean square (RMS) amplitude and mean power frequency (MPF) of the sEMG signal in the biceps brachii. Eleven subjects performed maximal isometric elbow flexion while indwelling and sEMG recordings were obtained from the biceps. The RMS amplitude and MPF of the surface signal, and the mean MUFR from the indwelling signal, were calculated over 500 ms epochs. Group means showed a strong MUFR-RMS amplitude relationship (r (2) = 0.91), but a weak MUFR-MPF relationship (r (2) = 0.20). Using all trials, the MUFR-RMS amplitude (r (2) = 0.19) and MUFR-MPF (r (2) = 0.0037) relationships were much weaker. Within individual subjects, the MUFR-RMS amplitude (mean r (2) = 0.13 +/- 0.17) and the MUFR-MPF (mean r (2) = 0.040 +/- 0.041) relationships were also weak. These results suggest that MUFR cannot be predicted from the characteristics of the sEMG signal.

Effect of Induced Functional Asymmetry on the Bilateral Deficit

Asymmetrical force production in homologous limbs may affect the magnitude of the bilateral deficit, but this influence is not well understood. PURPOSE: To determine the effect of an induced functional asymmetry on the bilateral deficit. METHODS: Twenty participants (age 28.4 ± 11.7 years) completed unilateral and bilateral isometric elbow flexion trials at 100% and 50% of maximal effort with the forearms supinated and pronated. Eight subjects' ability to produce maximal isometric elbow flexion force was impaired when the forearm was pronated. For these subjects, unilateral maximum isometric elbow flexion force was reduced by 10.0 ± 6.8% in the dominant arm and 13.0 ± 6.3% in the non-dominant arm when pronated. Bilateral indices for these subjects were calculated for each bilateral condition at both intensities. The indices were compared using a 2 × 4 (intensity × condition) repeated measures ANOVA. RESULTS: Maximal and submaximal effort bilateral indices were significantly less than zero (p<0.05) for all conditions, indicating the presence of bilateral deficits (Table 1), but none were significantly different from each other. Pronating the dominant arm increased the bilateral deficit by 5.5% (ES = .60) at maximal effort and 5.7% (ES = .47) at submaximal effort while pronating the non-dominant arm increased the deficit by 9.3% (ES = .56) only for the submaximal effort.Table 1: Bilateral indices for symmetrical and asymmetrical isometric elbow flexion trials.CONCLUSION: Compromising one limb's ability to produce force increases the size of the bilateral deficit at maximal and submaximal intensities.

Adaptations during familiarization to resistive exercise

This study focused on adaptations during familiarization to resistive exercise. It was also determined if familiarization requires one or more sessions. Twenty-six sedentary, college-aged females were matched and randomly assigned to one of two groups. Measurements were obtained during the initial familiarization period (Group 1: 15 trials on 1 day, Group 2: 5 trials on each of three consecutive days), and during retention tests scheduled two weeks and 3 months after the first test session. Elbow flexion torque and surface electromyography (SEMG) of the biceps and triceps were monitored concurrently. There were no significant differences between groups for any of the criterion measures. There was a significant ( p < 0.05) increase (12.4 Nm, or 38.8%) in maximal isometric elbow flexion torque. Biceps (agonist) root-mean-square (RMS) SEMG exhibited a significant ( p < 0.05) increase of 95 μV (29%). Triceps (antagonist) RMS SEMG underwent alternating decreases then increases, and each change was significant ( p < 0.05). The ratio of biceps to triceps RMS SEMG was used to assess cocontraction, and it followed the same pattern of change as triceps RMS SEMG. We concluded that both groups responded in the same way to testing, regardless of the pattern of the first 15 contractions. The increase in maximal isometric elbow flexion torque was due to neural drive to the bicep (agonist). There was a low level of triceps (antagonist) cocontraction to provide joint stability, and it was adjusted throughout the duration of testing.

Training Distribution And The Acquisition Of Maximal Isometric Elbow Flexion Strength

PURPOSE This study compared massed versus distributed muscle contractions in the acquisition of maximal isometric elbow flexion strength, to understand the role of motor learning in resistive exercise. METHODS Twenty-six sedentary, collegeaged females were matched and randomly assigned to one of two groups. The massed group (n=13) completed 15 maximal isometric elbow flexion strength trials in one session, while the distributed group (n=13) performed five such contractions on three successive days. After a 2-week and 3 month rest interval, both groups returned to perform another five maximal isometric elbow flexion strength trials to assess retention of any potential strength gains. Elbow flexion torque and surface electromyography (SEMG) of the biceps and triceps were monitored concurrently. RESULTS There was a significant (P <0.05) increase in strength in both groups from Block 1 (first 5 contractions) to Block 2 (first retest) and from Block 1 to Block 3 (second retest). Both groups exhibited a an increase (P <0.05) in biceps root-mean-square (RMS) SEMG amplitude. A significant (P <0.05) decrease in triceps RMS SEMG amplitude was found between Block 1 and Block 2 for both groups. However, a significant (P <0.05) increase was found between Block 2 and 3. CONCLUSIONS These results suggest that there is flexibility in resistive exercise schedules. There was a continued increase in neural drive to the agonist muscle throughout testing. This was accompanied by a reduction in antagonist coactivation that was a short-term (2-weeks) training effect, dissipated over the longer rest interval (3-months).

Training Distribution And The Acquisition Of Maximal Isometric Elbow Flexion Strength

PURPOSE This study compared massed versus distributed muscle contractions in the acquisition of maximal isometric elbow flexion strength, to understand the role of motor learning in resistive exercise. METHODS Twenty-six sedentary, collegeaged females were matched and randomly assigned to one of two groups. The massed group (n=13) completed 15 maximal isometric elbow flexion strength trials in one session, while the distributed group (n=13) performed five such contractions on three successive days. After a 2-week and 3 month rest interval, both groups returned to perform another five maximal isometric elbow flexion strength trials to assess retention of any potential strength gains. Elbow flexion torque and surface electromyography (SEMG) of the biceps and triceps were monitored concurrently. RESULTS There was a significant (P <0.05) increase in strength in both groups from Block 1 (first 5 contractions) to Block 2 (first retest) and from Block 1 to Block 3 (second retest). Both groups exhibited a an increase (P <0.05) in biceps root-mean-square (RMS) SEMG amplitude. A significant (P <0.05) decrease in triceps RMS SEMG amplitude was found between Block 1 and Block 2 for both groups. However, a significant (P <0.05) increase was found between Block 2 and 3. CONCLUSIONS These results suggest that there is flexibility in resistive exercise schedules. There was a continued increase in neural drive to the agonist muscle throughout testing. This was accompanied by a reduction in antagonist coactivation that was a short-term (2-weeks) training effect, dissipated over the longer rest interval (3-months).

The reversal of antagonists facilitates the peak rate of tension development

Gabriel DA, Basford JR, An K-N. The reversal of antagonists facilitates the peak rate of tension development. Arch Phys Med Rehabil 2001;82:342-6. Objective: The present study was designed to test the effects of the reversal of antagonists on the peak rate of tension development (dF/dtmax) of the elbow extensors. Design: Experimental, with matched controls. Setting: A biomechanics research laboratory. Participants: Twenty-six healthy women without a history of upper extremity injury or neurologic disorder, randomly assigned to experimental (n = 13) or control (n = 13) groups. Interventions: Two groups of healthy subjects followed identical exercise protocols, except that the control group performed maximal isometric contractions of the elbow extensors and the experimental group executed a maximal isometric elbow flexion contraction immediately before a maximal elbow extension contraction. Both groups performed 5 cycles of a 2-second contraction with 22-second rest periods between agonist muscle contractions and were evaluated at 4 test sessions spaced 2 weeks apart. Main outcome measures: All measurements were done with the shoulder and elbow at 90° of flexion in the sagittal plane to ensure reproducibility. A load cell was used to measure elbow extension moment and to calculate the peak rate of tension development (dF/dtmax). Biceps and triceps brachii surface electromyographic activity was monitored concurrently. The electromyographic measures were mean spike (peak-to-peak) amplitude and mean spike frequency of the biceps and triceps brachii activity. Results: Intraclass dF/dtmax and electromyographic reliability was good (r ≥.72) in both groups. Because biceps electromyographic measures were considerably less reliable (r ≤.53), they were not included in our analysis. While dF/dtmax increased quadratically in both groups (p <.05), the experimental group was on average 36.1Nm · s−1 (63%) greater across sessions 2 to 4 (p <.05). In contrast, triceps electromyographic activity did not differ significantly between groups (p >.05). The means averaged across groups exhibited a quadratic increase from session 1 to session 4: 91μV or 48% for mean spike amplitude (p <.05) and 7Hz or 16% for mean spike frequency (p <.05). Conclusions: The greater dF/dtmax for the experimental group was not associated with increased electromyographic activity. The experimental group appeared to use the biomechanic properties of the pretensioned extensor muscle-tendon complex, rather than neurologic biasing, to accomplish its power gains.

Characteristics of muscle activities in a quick change in magnitude of force.

The present study was designed to examine the characteristics of muscle activities in a quick voluntary change in magnitude of force. 15 subjects were asked to change their magnitude of force from 50% of maximal isometric elbow-flexion strength (MVS) to 20% MVS as quickly as possible. On each EMG of biceps and triceps, a period with no muscle activity was observed. It seems that the occurrence of the pause in muscle activity on EMG contributes to more quick change in magnitude of exerted force.

Window accidents.

<h3>Objective</h3> To evaluate whether deficits of elbow flexor and extensor muscle strength exist in lateral epicondylalgia (LE) in comparison with a healthy control population. <h3>Design</h3> Cross-sectional study. <h3>Participants</h3> 150 participants with unilateral LE were compared with 54 healthy control participants. <h3>Main outcome measures</h3> Maximal isometric elbow flexion and extension strength were measured bilaterally using a purpose-built standing frame such that gripping was avoided. <h3>Results</h3> The authors found significant side differences in elbow extensor (−6.54 N, 95% CI −11.43 to −1.65, p=0.008, standardised mean difference (SMD) −0.45) and flexor muscle strength (−11.26 N, 95% CI −19.59 to −2.94, p=0.009, SMD −0.46) between LE and control groups. Within the LE group, only elbow extensor muscle strength deficits between sides was significant (affected–unaffected: −2.94 N, 95% CI −5.44 to −0.44). <h3>Conclusion</h3> Small significant deficits of elbow extensor and flexor muscle strength exist in the affected arm of unilateral LE in comparison with healthy controls. Notably, comparing elbow strength between the affected and unaffected sides in unilateral epicondylalgia is likely to underestimate these deficits. <h3>Trial Registration</h3> Australian New Zealand Clinical Trials Register ACTRN12609000051246.