Differences in Muscle Fatigability of Vastus Medialis between Sexes Using Surface Electromyographic Power Spectral Analysis in Healthy Adults.

Objectives: With a relatively high percentage of type I fibers in the vastus medialis (VM), its fatigability may be more sensitive to the effects of muscle activity in the quadriceps. However, sex-related differences in the muscle fatigability of the VM remain unknown. The purpose of the present study was to assess the differences in fatigability of the VM between healthy adult men and women. Methods: Surface electromyographic (EMG) activities of VM oblique (VMO) and VM long (VML) were recorded during sustained isometric contraction on a leg press machine. The results of EMG power spectral analysis were compared between healthy adult men and women. The decline in the median frequency (MF), defined as MF slope, was calculated using spectrum analysis after fast Fourier transform of the raw EMG signals of VMO and VML. Results: The endurance time and the MF slopes of the VMO and VML were significantly longer and lower, respectively, in women than in men. The present results demonstrated that both VMO and VML are more fatigue-resistant in women than in men. Conclusions: Understanding the sex differences in fatigability could help to design more effective exercise regimens for VMO and VML in healthy individuals. A similar approach should be considered when prescribing practical exercise regimens for patients with muscle atrophy.

Comparison of erector spinae fatigability between female patients with Parkinson's disease and healthy individuals: a cross sectional pilot study.

BACKGROUND: Postural abnormality is one of the main symptoms of Parkinson's disease (PD). The erector spinae muscles play an important role in maintaining an upright posture, but the fatigability of the erector spinae in patients with PD is unknown. The purpose of this study was to compare the trunk extension maximum voluntary contraction (MVC) and the fatigability of the erector spinae between female patients with PD and healthy volunteers. METHODS: Th participants of this cross-sectional pilot study comprised 19 patients with PD and nine healthy volunteers matched for sex, age, and physical characteristics as a control group. The MVC of all participants was measured, and after sufficient rest, the Sørensen back endurance test was conducted to the point of exhaustion. The muscle activity of the erector spinae during the Sørensen back endurance test was measured using surface electromyography. The median frequency (MF) slope, which is an index of fatigability, was calculated from the recorded surface muscle activity by means of power spectrum analysis using a Fast Fourier transformation. RESULTS: Nine of the 19 patients with PD were unable to perform the Sørensen back endurance test, and a lower proportion of the PD group were able to perform it compared with the control group. The MVC of those patients with PD who were able to perform the Sørensen back endurance test was lower than that of the control group, and the time for which the pose could be maintained was shorter. There was no significant difference between the MF slope on the left and right side in the PD group, and it was higher on both sides than in the control group. CONCLUSION: This is the first study to demonstrate a reduction of maximum muscle strength and great fatigability of the erector spinae in patients with PD. This discovery strongly underlines the need for paraspinal muscle training from an early stage with the aim of preventing the progression of postural abnormality in patients with PD.

Differences in fatigability of vastus medialis muscle between patients with limb symmetry index of <90% and ≥90% after chronic anterior cruciate ligament reconstruction.

BACKGROUND: A limb symmetry index (LSI) of ≥90% for the quadriceps is recommended for return to sports activity after anterior cruciate ligament reconstruction (ACLR). However, there is no information on differences in muscle fatigability between patients with LSI of <90% and ≥90%. The aim of this study was to assess the difference in quadriceps muscle fatigability on the involved side between post-ACLR patients with LSI of <90% and ≥90%. We hypothesized that there were differences between the two groups in muscle fatigability on the involved side reflecting difference in muscle fiber composition in the vastus medialis (VM) muscle. METHODS: The study subjects were 18 adult men who had undergone ACLR followed by rehabilitation therapy. LSI was <90% in 10 and ≥90% in 8 adult men. Surface electromyography (EMG) of the VM muscle was recorded during sustained quadriceps muscle isometric contraction. The median frequency (MF) was computed from the raw EMG signal using fast Fourier transform spectrum analysis. The MF slope was also calculated. RESULTS: There were no differences in anthropometric characteristics, time since ACLR, anterior tibial translation and peak torque of knee extension on the involved side between the two groups. However, MF slope was significantly lower in the LSI ≥ 90% group than the <90% group. CONCLUSION: Our results demonstrated fatigue-resistant vastus medialis in post-ACLR patients with LSI ≥90% compared to those with LSI <90%. The finding adds support to the use of ≥90% as the cutoff value for LSI for return of post-ACLR patients to sports activity.

Nutritional status and activities of daily living in patients with Parkinson's disease.

Patients with Parkinson's disease are often frail and likely to be malnourished. Several studies have reported the adverse effects of malnutrition on functional outcomes; however, the association between nutritional status and activities of daily living is unclear among patients with Parkinson's disease. This study aimed to investigate the relationship between nutritional status and activities of daily living in patients with Parkinson's disease. We conducted a retrospective cohort study with the data of 124 patients who were consecutively admitted to a rehabilitation hospital in Japan, among whom the data of 61 patients were included in the analyses. The Controlling Nutritional Status score was used to measure the nutritional status of the participants, and the motor subdomain of the Functional Independence Measure was used to assess the activities of daily living. Piecewise linear mixed-effects models were fitted to the data after adjusting for confounding factors. A poor nutritional status (i.e., Controlling Nutritional Status score >3) was significantly associated with a poor Functional Independence Measure gain, which was defined as difference in the score values of the Functional Independence Measures between discharge and admission. Our findings could aid in developing nutritional intervention programs for patients with Parkinson's disease by employing the Controlling Nutritional Status score to improve their activities of daily living.

Increased oxytocin-monomeric red fluorescent protein 1 fluorescent intensity with urocortin-like immunoreactivity in the hypothalamo-neurohypophysial system of aged transgenic rats.

To visualize oxytocin in the hypothalamo-neurohypophysial system, we generated a transgenic rat that expresses the oxytocin-monomeric red fluorescent protein 1 (mRFP1) fusion gene. In the present study, we examined the age-related changes of oxytocin-mRFP1 fluorescent intensity in the posterior pituitary (PP), the supraoptic nucleus (SON) and the paraventricular nucleus (PVN) of transgenic rats. The mRFP1 fluorescent intensities were significantly increased in the PP, the SON and the PVN of 12-, 18- and 24-month-old transgenic rats in comparison with 3-month-old transgenic rats. Immunohistochemical staining for urocortin, which belongs to the family of corticotropin-releasing factor family, revealed that the numbers of urocortin-like immunoreactive (LI) cells in the SON and the PVN were significantly increased in 12-, 18- and 24-month-old transgenic rats in comparison with 3-month-old transgenic rats. Almost all of urocortin-LI cells co-exist mRFP1-expressing cells in the SON and the PVN of aged transgenic rats. These results suggest that oxytocin content of the hypothalamo-neurohypophysial system may be modulated by age-related regulation. The physiological role of the co-existence of oxytocin and urocortin in the SON and PVN of aged rats remains unclear.

Properties of Paraspinal Muscles in Japanese High School Baseball Players With Terminal-Stage Lumbar Spondylolysis.

BACKGROUND: Lumbar spondylolysis is a defect in the pars interarticularis that is common in young athletes; the stress distribution at the pars interarticularis is the highest in extension and rotation movements. The paraspinal muscles play an important role in stabilization of the lumbar spine; however, no study has assessed the properties of paraspinal muscles in athletes with lumbar spondylolysis. OBJECTIVE: To evaluate the properties of paraspinal muscles in athletes with lumbar spondylolysis. DESIGN: Cross-sectional study. SETTING: Laboratory. PARTICIPANTS: Six high school baseball players with terminal-stage lumbar spondylolysis and 11 high school baseball players without organic lumbar lesions of similar anthropometric characteristics. METHODS: All subjects performed the unsupported trunk holding test combined with surface electromyographic (EMG) power spectral analysis until exhaustion. The results of EMG power spectral analysis were compared between the spondylolysis and control groups. MAIN OUTCOME MEASUREMENTS: The median frequency (MF) was computed from the raw EMG signal of the erector spinae and multifidus during trunk holding test using fast Fourier transform spectrum analysis. The initial MF and MF slope were calculated. RESULTS: No significant differences in endurance time were found between the spondylolysis and control groups. The initial MF and the MF slopes of the erector spinae and multifidus were significantly lower in the spondylolysis group than in the control group. CONCLUSIONS: The results suggest lower fast-twitch motor unit recruitment in the erector spinae and multifidus of high school baseball players with terminal-stage lumbar spondylolysis compared with the control. LEVEL OF EVIDENCE: IV.

Fatigue-related differences in erector spinae between prepubertal children and young adults using surface electromyographic power spectral analysis.

BACKGROUND: The erector spinae is more resistant to fatigue in adult women than men. However, no study has reported the sex differences in back muscle fatigue in children. OBJECTIVE: The aim of this study was to evaluate the fatigability of erector spinae in prepubertal children and adults, in both males and females. METHODS: Fourteen prepubertal boys, 13 prepubertal girls, 14 adult men, and 13 adult women performed the Sørensen back isometric endurance test until exhaustion. The results of electromyographic (EMG) power spectral analysis of erector spinae were compared between both age groups and sexes. RESULTS: The slopes of EMG power spectral median and mean power frequency were significantly higher in males than in females, in both age groups. Furthermore, the slopes were significantly lower in prepubertal children than in adults, in both males and females. CONCLUSIONS: Our results showed major differences in the fatigue threshold of the erector spinae between boys and girls and children and adults. The muscle fatigued faster in prepubertal boys and adult men than in prepubertal girls and adult women. In both sexes, a lower slope of EMG power spectrum parameters of the erector spinae was noted during endurance test in prepubertal children compared to adults.

Age-related sex differences in erector spinae muscle endurance using surface electromyographic power spectral analysis in healthy humans.

BACKGROUND CONTEXT: Previous studies reported that the erector spinae muscle is more resistant to fatigue in healthy adult women than in men. However, no study has reported changes in back muscle fatigue with aging in healthy men and women. PURPOSE: The aim of this study was to evaluate age-related changes in muscle fatigue of erector spinae muscle in men and women. STUDY DESIGN/SETTING: This cross-sectional study was conducted in a laboratory. PATIENT SAMPLE: Fifty-three healthy subjects (11 elderly men, 11 elderly women, 17 young men, and 14 young women) without low back pain history. OUTCOME MEASURES: The median frequency (MF) and mean power frequency (MPF) during trunk holding test were derived from the raw electromyographic (EMG) signal using Fast Fourier Transform spectrum analysis program. The rates of changes in MF and MPF were calculated. METHODS: Subjects performed the unsupported trunk holding test until exhaustion. The results of power spectral analysis of the EMG activity of the left erector spinae muscle were compared in both age groups and sexes. RESULTS: The endurance time in young men was significantly shorter than in young women. The slopes of MF and MPF in young men were significantly higher than in young women. There were no significant differences in MF and MPF slopes of elderly men and elderly women. Furthermore, the MF and MPF slopes were significantly lower in elderly men than young men but similar in the two women groups. CONCLUSIONS: Age-related changes in the slopes of MF and MPF of erector spinae muscle occur in healthy men but not in healthy women.

Muscle maintenance by volitional contraction against applied electrical stimulation.

Muscle training exercises are needed for muscular endurance during spaceflight. This study was designed to investigate effects of volitional contraction against applied electrical stimulation on the muscular endurance of the proximal upper extremity. Thirteen healthy sedentary men were allocated into two groups. One group participated in a hybrid (HYB) exercise regimen in which the biceps brachii was stimulated as he volitionally extended his elbow, and the triceps brachii was stimulated as the volitionally flexed his elbow. The second group underwent a similar regimen in which the electrical stimulation (ELS) was alternatively delivered to the biceps brachii and then to the triceps brachii with the limb fixed. Forty-second surface electromyography (EMG) recordings at 50% maximum voluntary contraction (MVC) were made as baseline data at just before starting the training regimen, and again conclusion. The median frequency (MF) and mean power frequency (MPF) slopes with time were determined using power spectrum analysis. There were statistical significance only for the triceps in which the MF and MPF slopes in the HYB Group became less negative over the period of study (from -45.7+/-14.7 and -47.0+/-8.6%/min at baseline to -36.9+/-10.7 and -36.8+/-7.0%/min at the end of training, respectively). The corresponding values for these slopes in the ELS Group showed opposite tends with less marked changes of borderline significance for MF and of statistical significance for MPF. These results suggested that the HYB exercise regimen was capable of producing an improvement in triceps but not biceps brachii.

Muscle training by means of combined electrical stimulation and volitional contraction.

INTRODUCTION: A variety of techniques have been used with variable success in an attempt to reverse the loss of muscle strength, bulk, and endurance that occurs during spaceflight. This study was designed to evaluate a new "hybrid" approach that uses the resistance provided by an electrically stimulated antagonist muscle to resist the volitional contraction of its agonist. METHODS: There were 20 subjects who were randomized into 3 groups that received either the new hybrid program (HYB), isotonic weight training (WT), or isometric electrical stimulation (ES). Subjects trained 3 times per week for 8 wk with each session consisting of their non-dominant upper extremity performing 10 sets of 10 reciprocal 2-s elbow flexion and extension contractions separated by 1-min rest intervals. Elbow flexion\extension torques and biceps\triceps cross-sectional areas (CSA) were measured at the beginning, midpoint, and end of training as well as at follow-up 4 wk later. RESULTS: The HYB group demonstrated statistically significant increases in elbow flexion and extension torques (56% and 31%, respectively) at the end of training that were similar to or larger than the gains in the other groups with benefits that persisted at follow-up 4 wk later. Muscle CSA increases in the HYB group (10%) were comparable or larger than those in WT and ES subjects. CONCLUSIONS: These results suggest that HYB training may be an effective way to maintain and increase muscle bulk and strength for patients during bed rest, as well as astronauts in space.

Improvement in knee extension strength through training by means of combined electrical stimulation and voluntary muscle contraction.

Weight training (WT) is the most common method of maintaining and increasing muscle strength. WT, however, is not always useful as it requires the external resistance and stabilization. We have developed a "hybrid training" (HYB) approach that avoids these problems by using electrically stimulated muscles to provide resistance to the motion of a muscle undergoing training. Here we report the efficacy of HYB compared with conventional WT for increasing the muscle strength around the knee at both slow and fast joint speeds (at 30 and 180 degrees /sec). Two matched groups, each of 8 healthy men aged 22 years, exercised 3 times/week for six weeks. Both groups showed significantly increased strength in concentric torque at 30 degrees /sec (HYB +28%, WT +33%) and at 180 degrees /sec (HYB +33%, WT +38%), and also in eccentric torque at 30 degrees /sec (HYB +25%, WT +24%) and at 180 degrees /sec (HYB +19%, WT +30%) (p < 0.001). HYB is comparable with WT exercising with the exception of high-speed contractions, while HYB has a clear advantage in not needing external resistance equipment or stabilization. HYB is therefore considered a useful approach for strengthening muscles when a person is restricted to bed rest or during space flight.

Effects of a hybrid exercise on the activities of myogenic enzymes in plasma.

"Hybrid" exercise uses forces generated by an electrically stimulated muscle to resist the motion of a volitionally contracting agonist. This approach is effective in increasing muscle bulk and strength. Its safety, however, has not been studied and the purpose of this study was to address this lack by assessing the impact of a hybrid strengthening regimen on the serological markers of exercise associated muscle damage. Twelve healthy, sedentary men between the ages of 20 and 27 years were divided into two groups of 6. The members of each group completed an exercise session that consisted of 10 sets of 10 reciprocal elbow flexor and extensor contractions separated by 1-minute rest intervals. In one group, the subjects underwent a hybrid exercise protocol. Subjects in the second group underwent a conventional isometric electrical stimulation program with the same stimulation intensities. Plasma creatine kinase (CK), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) activities were determined immediately before and after the exercise session as well as at follow-up 1, 2, and 7 days later. Secondary variables included active and passive range of motion and the subjects' perceived levels of "soreness" . Evaluation revealed that neither enzymatic activities nor range of motion changed in a statistically significant manner with time within the groups or between the groups. In conclusion, the stimulation intensities involved in hybrid exercise programs of the upper extremity do not appear to be associated with either overt or covert signs of muscle injury.

Muscle sympathetic nerve activity during isometric exercise in patients with cerebrovascular accidents.

OBJECTIVES: To define isometric exercise-induced pressor responses in patients with cerebrovascular accidents (CVAs) and to assess potential cardiovascular and sympathetic nervous system abnormalities during isometric exercise in CVA. DESIGN: Nonrandomized study. SETTING: University laboratory setting. PARTICIPANTS: Eight men with CVA who had documented damage of subcortical structures and 8 sex-matched controls. INTERVENTIONS: A 2-minute sustained contraction of elbow flexor muscles in the unaffected side at 35% of maximal voluntary contraction (MVC; isometric exercise). MAIN OUTCOME MEASURES: Heart rate, arterial blood pressure, and muscle sympathetic nerve activity (MSNA), recorded from the peroneal nerve on the affected side. RESULTS: The percent changes in total MSNA, heart rate, and mean blood pressure in patients with CVA increased during isometric exercise but were attenuated compared with the controls. Total MSNA (mean burst amplitude per minute times burst rate) increased significantly in CVA and control subjects during isometric exercise by 18.7%+/-6.3% and 95.8%+/-25.2%, respectively. CONCLUSIONS: The attenuated pressor responses during isometric exercise in subjects with CVA relative to the controls indicated damage to subcortical structures; such damage lowered sympathetic nervous response to isometric exercise. Our findings suggest that isometric exercise at 35% of MVC does not put patients with CVA at risk for serious tachycardia or hypertension.

Development of practical and effective hybrid exercise for use in weightless environment.

Bedrest and spaceflight are associated with profound losses of muscle bulk and strength which hinder patient's or astronaut's health and reintegration into daily life. We attempted to do two things in this small pilot study. First, we assessed the potential of hybrid electrical stimulation-volitional contraction exercise program to increase proximal lower extremity strength, muscle bulk, and bone mineral density (BMD). Second, we assessed the utility of unilateral lower limb suspension (ULLS) in producing losses in these quantities comparable to those that occur during bedrest and spaceflight. More specifically, this study made an initial evaluation of (1) ability of hybrid exercise program to preserve knee extensor and flexor maximum volitional contraction (MVC), cross-sectional area (CSA), and BMD in 4 healthy men between ages of 22 and 24, and (2) utility of ULLS in producing decrements in these parameters similar to those that occur in weightless environment in single 38 year-old male. Results show that CSA of rectus femoris and hamstrings increased about 5.3% and femoral BMD by 7%. MVC may have exhibited a more complex behavior with 3.0% at end of training, followed by 9.3% at follow-up. ULLS resulted in dramatic losses of strength (70%), CSA (4.8%), and BMD (8.2%).

Agonist contractions against electrically stimulated antagonists.

OBJECTIVE: To assess an exercise program that uses electrically stimulated antagonists to resist agonist muscle contractions. DESIGN: In 1 limb, electrically stimulated antagonists resisted elbow flexion and extension. In the other, stimulation occurred without volitional muscle contraction. SETTING: A biomechanics laboratory in Japan. PARTICIPANTS: Twelve men between the ages of 19 and 24 years. Subjects served as their own controls. INTERVENTION: Subjects trained 3 times a week for 12 weeks. Each session consisted of 10 sets of 10 elbow flexor and extensor contractions. MAIN OUTCOME MEASURES: Isokinetic elbow extension and flexion torques. Biceps and triceps brachii cross-sectional areas. RESULTS: Elbow extension torques increased (32.85% at 30 degrees/s, 27.20% at 60 degrees/s, 26.16% at 90 degrees/s; all P

Cardiovascular and endocrine responses during the cold pressor test in subjects with cervical spinal cord injuries.

OBJECTIVE: To investigate cardiovascular regulation and endocrine responses during the cold pressor test in patients with chronic spinal cord injury (SCI). DESIGN: Experimental and control study. SETTING: University laboratory, department of rehabilitation medicine, in Japan. PARTICIPANTS: Eight quadriplegic subjects with complete spinal cord transection at the C6 to C8 level and 6 age-matched healthy subjects. INTERVENTIONS: Cardiovascular and endocrine responses were examined during 2 minutes of control, 3 minutes of ice-water immersion of the foot, followed by a 3-minute recovery. MAIN OUTCOME MEASURES: Blood pressure, heart rate, the Borg 15-point Rating of Perceived Pain Scale, and blood samples for measurement of plasma norepinephrine, epinephrine, plasma renin activity, plasma aldosterone, and arginine vasopressin. RESULTS: The rise in the mean arterial blood pressure during the cold pressor test in patients with SCI (baseline, 81.6+/-3.7mmHg; increased by 30%+/-6.1%) was significantly (P<.05) higher than that in healthy subjects (baseline, 101.2+/-4.5mmHg; increased by 20%+/-4.5%). The SCI subjects had no change in heart rate throughout the test, in contrast to the tachycardia noted in normal subjects. Baseline plasma norepinephrine in SCI subjects (63.0+/-18.3pg/mL) was significantly lower than in normal subjects (162.3+/-19.6pg/mL) and plasma norepinephrine increased significantly during the cold pressor test in both groups. CONCLUSIONS: In the SCI subjects, a reflex sympathetic discharge through the isolated spinal cord results in a more profound rise in mean blood pressure during ice-water immersion. This response was free of inhibitory impulses from supraspinal center and baroreceptor reflexes, either of which might restrain the increase in blood pressure.