Neuromuscular responses of the plantar flexors to whole-body vibration.

Enhanced physical performance following whole-body vibration (WBV) has been attributed to increased muscle activity; however, few studies have measured the mechanisms underlying these changes. The objective of this study was to measure the responsiveness of the Ia pathway as well as contractile properties in 16 young adults (24±2 years, eight men, eight women) following repeated bouts of acute WBV (45 Hz, 2 mm). Hoffman reflexes (H-reflex), compound muscle action potentials (M-wave), and twitch contractile properties were measured prior to and immediately following five 1-minute WBV exposures, and at 3, 5, 10, and 20 minute post-WBV. M-wave and H-reflex amplitudes decreased by 8% (P<.001) and by 46% (P<.05), respectively, whereas peak twitch torque decreased by 9% (P<.01) and rate of twitch torque development slowed 8% (P<.05). Percent voluntary activation and maximal plantar flexor torque were unchanged as a consequence of WBV (P>.05). In response to acute WBV, the root mean square of the soleus electromyography signal (EMGRMS ) increased by 8%, while the EMGRMS of the lateral gastrocnemius increased by 3% (P<.05). These data indicate that the responsiveness of the Ia pathway is diminished and contractile function is impaired immediately following WBV, and that the neural mechanisms underlying improved performance following WBV lie in alternative hypotheses possibly involving spindle disfacilitation or Golgi afferent modulation.

Duration of fascicle shortening is affected by muscle architecture and sex.

PURPOSE: The purpose of this study was to examine muscle fascicle properties of the gastrocnemius medialis (GM) during contraction and stretch between males and females. During contraction muscle fascicles shorten and pennation angles increase to generate force. Due to the elastic nature of the attached tendon, the fascicles continue to shorten when maximal force is achieved in order to sustain isometric force and this duration of fascicle shortening (DFS) can be observed with ultrasonography. Linear and curved muscle fascicles both display these kinetics; however, it is currently unknown if static stretch prior to a maximal voluntary contraction (MVC) alters the DFS and whether the effect differs between males and females. METHODS: Subjects performed an isometric MVC of the plantar flexors before and after a 2-min maximal dorsi-flexion stretch. Plantar flexor force was measured and ultrasound videography used to record GM and Achilles tendon architecture. RESULTS: Males were stronger than females (p = 0.004). The DFS was longer for females compared to males (p = 0.001) and the addition of a static stretch increased the DFS for curved (p = 0.002), but not linear, fascicles. Curved fascicles were longer (p = 0.05) with larger pennation angles (p = 0.04) for both males and females when compared to linear fascicles. Tendon excursion was greater (p = 0.05) post-stretch during contraction when compared to pre-stretch. CONCLUSIONS: This study provides evidence that regardless of sex, curved muscle fascicles behave differently than linear fascicles and should be considered separately when muscle architecture is examined.

The effect of tendon vibration on motor unit activity, intermuscular coherence and force steadiness in the elbow flexors of males and females.

BACKGROUND: Compartmentalized responses in motor unit (MU) activity of the short head (SH) and long head (LH) of the biceps brachii are observed following forearm position change. Differential muscle spindle afferent distribution has been proposed as a potential mechanism underlying this behaviour. Tendon vibration is an effective, non-invasive method of increasing muscle spindle afferent activity of a target muscle group offering a paradigm in which this hypothesis may be investigated further. AIM: To determine the effect of tendon vibration on MU recruitment and discharge rates of the SH and LH, muscle activity of the elbow flexors and triceps brachii, intermuscular coherence among the SH, LH, brachioradialis and triceps brachii and force steadiness in young males and females during isometric elbow flexion. METHODS: Intramuscular electromyography (EMG) of the SH and LH, and surface EMG of the elbow flexors were recorded pre- and post-vibration during low-force isometric contractions. Motor unit recruitment thresholds, MU discharge rates and MU discharge variability; surface EMG amplitude, intermuscular coherence and force steadiness were determined pre- and post-vibration. RESULTS: Differential changes in all MU properties, EMG amplitude and intermuscular coherence were observed among elbow flexors. Although MU properties exhibited differential changes, they accounted for little variance in isometric force steadiness. However, intermuscular EMG coherence among all muscles investigated was reduced post-vibration. CONCLUSION: Uncoupling of common oscillatory input as a result of differential muscle spindle afferent inputs to elbow flexors may be responsible for the reduction in force steadiness following tendon vibration and a forearm position change.

Short interspike intervals and double discharges of anconeus motor unit action potentials for the production of dynamic elbow extensions.

Incidence of double discharges (DDs; >100 Hz) and short interspike intervals (ISIs; >50 to <100 Hz) is reported to vary widely among different muscles and tasks, with a higher incidence in motor unit (MU) trains of fast muscles and for the production of fast contractions in humans. However, it is unclear whether human muscles with a large composition of slower motor units exhibit DDs or short ISIs when activated with maximal synaptic drive, such as those required for maximal velocity dynamic contractions. Thus the purpose of this study was to determine the effect of increasing peak contraction velocity on the incidence of DDs and short ISIs in the anconeus muscle. Seventeen anconeus MUs in 10 young males were recorded across dynamic elbow extensions ranging from low submaximal velocities (16% of maximal velocity) up to maximal velocities. A low incidence of DDs (4%) and short ISIs (29%) was observed among the 583 MU trains recorded. Despite the low incidence in individual MU trains, a majority (71% and 94%, respectively) of MUs exhibited at least one DD or short ISI. The number of short ISIs shared no variance with MU recruitment threshold (R(2) = 0.02), but their distribution was skewed toward higher peak velocities (G = -1.26) and a main effect of peak elbow extension velocity was observed (P < 0.05). Although a greater number of short ISIs was observed with increasing velocity, the low incidence of DDs and short ISIs in the anconeus muscle is likely related to the function of the anconeus as a stabilizer rather than voluntary elbow extensor torque and velocity production.

Motor unit properties from three synergistic muscles during ramp isometric elbow extensions.

Many tasks require synergistic activation of muscles that possess different architectural, mechanical, and neural control properties. However, investigations of the motor unit (MU) mechanisms which modulate force are mostly restricted to individual muscles and low forces. To explore the pattern of MU recruitment and discharge behavior among three elbow extensors (lateral and long heads of the triceps brachii, and anconeus) during ramp isometric contractions, recruitment thresholds of 77 MUs in five young men were determined and corresponding MU discharge rates were tracked in 1-s epochs over forces ranging from 0 to 75 % of maximal voluntary isometric force (MVC). Across all forces, MUs in the lateral head discharged at higher rates than those in the anconeus (p < 0.001, Δ = 0.23). When all MUs were considered, recruitment thresholds in the long head of the triceps brachii were higher than the lateral head (p < 0.05, Δ = 0.70) with a trend (p = 0.08, Δ = 0.48) for higher recruitment thresholds in the long head compared with the anconeus. Together, these data indicate a potential mechanical disadvantage of the long head of the triceps brachii at 0° shoulder flexion. However, among low-threshold MUs (<10 % MVC), recruitment thresholds were lower in the anconeus than in both heads of the triceps brachii consistent with the expected twitch contractile and fiber type differences among these muscles. These findings illustrate the importance of considering synergistic relations among muscles used for a coordinated task, and the sensitivity of synergies to muscle architectural, mechanical, and possibly specific synaptic input factors.

Reduced motor unit discharge rates of maximal velocity dynamic contractions in response to a submaximal dynamic fatigue protocol.

Fatigability is highly task dependent wherein motor unit (MU) discharge rates and recruitment thresholds are affected differently depending on whether contractions are performed at maximal or submaximal intensities. Although much is described for isometric tasks, the behavior of MU properties during the production of maximal velocity dynamic contractions following submaximal fatiguing contractions is unknown. In seven young men, we evaluated changes in MU recruitment thresholds and MU discharge rates of the anconeus muscle during both submaximal and maximal dynamic elbow extensions following a submaximal dynamic fatiguing protocol of moderate intensity to velocity task failure. Velocity and power of the maximal dynamic contractions declined ∼45 and ∼55%, respectively, but these variables were unchanged for the submaximal target velocity contractions. Discharge rates of the 12 MUs at task failure were unchanged for submaximal dynamic contractions, but were decreased ∼20% for maximal dynamic and ballistic isometric contractions at task failure. MU recruitment thresholds of submaximal dynamic contractions decreased 52% at task failure, but were similar throughout the fatiguing protocol for maximal contractions. These findings support the concept of a common neural mechanism responsible for the relative declines in MU discharge rate associated with submaximal fatigability in both isometric and dynamic contractions.

Changes in motor unit recruitment thresholds of the human anconeus muscle during torque development preceding shortening elbow extensions.

Rate of torque development and the subsequent movement velocity are modulated by motor unit (MU) properties, primarily MU discharge rate and MU recruitment threshold (MURT). In isometric conditions, MURTs have been shown to decrease with increased rates of torque development. It is unclear whether this relationship is similar in the production of dynamic shortening contractions. Using fast joint velocities to drive the system, we aimed to determine how anconeus MURTs recorded during the torque production phase preceding movement were affected in relation to the resultant peak elbow extension velocity. Recruitment thresholds of 17 MUs from 9 young men were tracked throughout non-isokinetic dynamic elbow extensions with velocities ranging from 64°/s to 500°/s at a constant resistance of 25% of maximal voluntary isometric contraction and during isometric elbow extensions (0°/s). Relative MURTs decreased ∼50% from the slowest (<25% of maximal velocity) to the fastest (>75% of maximal velocity) resultant velocity ranges (P < 0.05). Although a significant (P < 0.001) but weak (r = -0.27, R(2) = 0.08) relationship was observed between MURT and resultant peak elbow extension velocity for the group, only 7 of the 17 MUs displayed significant moderate (r = -0.40, R(2) = 0.17) to strong (r = -0.85, R(2) = 0.73) negative MURT-velocity relationships. These data indicate variable responses of MURTs with increasing resultant peak velocity, which may be related to the intrinsic properties of individual MUs.

Age- and sex-related differences for electromyography gaps during daily activity and a discrete task.

Temporal patterns of quiescent electromyography termed 'gaps' were investigated in young and old men and women for a discrete task and daily activity. Gaps in women (1.3±3.2) and old adults (1.5±3.4) were fewer compared with men (4.7±6.7) and young adults (4.6±6.9) for the discrete task (p<0.001). Gap duration was shorter for women (0.1±0.2s) and old adults (0.1±0.3s) compared with men (0.2±0.3s) and young adults (0.2±0.2s) (p<0.01). For daily activity, gap number was similar with age, but gap duration and percentage of total time occupied by gaps were less in old compared with young adults (50%), and in women compared with men (43%) (p<0.001). Results suggest gap activity is sensitive to type and duration of activity and that old adults and women demonstrate less quiescent electromyography than young adults and men.

Motor unit discharge rates of the anconeus muscle during high-velocity elbow extensions.

Motor unit recruitment and motor unit discharge rate (MUDR) have been widely studied in isometric conditions but minimally during velocity-dependent contractions. For isometric contractions, surface electromyography (EMG) activity of the elbow extensors plateaus at near maximal torques (Le Bozec et al. 1980; Le Bozec and Maton 1982). One study (Maton and Bouisset 1975) recorded single motor unit (MU) activity at maximal velocities; however, only the rate of the first interspike interval (ISI) was reported and likely was not representative of the average MUDR of the MU train. The purpose was to calculate average MUDRs of the anconeus during loaded velocity-dependent contractions from zero velocity (isometric) up to maximal velocity (V(max25)) through a large range of motion. A Biodex dynamometer was used to record elbow extension torque, position, and velocity. Single MU potentials were collected from the anconeus with intramuscular EMG, and surface EMG was sampled from the lateral head of the triceps brachii during maximal voluntary isometric contractions (MVCs) and velocity-dependent contractions loaded at 25% MVC over 120° range of motion at five target velocities (0, 25, 50, 75, 100%V(max25)). Elbow extension velocities ranged from 93 to 494°/s and average MUDR ranged from 11.8 Hz at 25%MVC to 39.0 Hz at 100%V(max25.) Overall average MUDRs increased as a function of velocity, although the root mean square of triceps brachii surface EMG plateaued at 50%V(max25). Piecewise regression analysis revealed two distinct linear ranges each described by a unique equation, suggesting that MUDRs of the anconeus enter a secondary range of firing, characterized by a steeper slope as velocity approaches maximum.

Age independent and position-dependent alterations in motor unit activity of the biceps brachii.

In the biceps brachii, age-related differences in synaptic excitability and muscle architecture may affect motor unit (MU) activity differently depending on the position of the forearm. It was hypothesised that as a result of these age-related differences, greater changes in MU activity would accompany a change in forearm position in old when compared with young men. Six young (22 +/- 3 years) and six old (84 +/- 3 years) men maintained isometric elbow flexion at 10% of maximal voluntary contraction (MVC) during changes in forearm position. Forty-nine MUs in the short (SBB) and long (LBB) heads of the biceps brachii were followed. Motor unit recruitment and de-recruitment thresholds, motor unit discharge rates (MUDRs), and MU discharge variability were measured. Although an age-related decrease in MU recruitment thresholds, and increase in MU discharge variability was evident, changes in forearm position influenced MUDRs similarly in young and old men (P = 0.27). Motor unit recruitment thresholds of the SBB were highest in the pronated position (8.2 +/- 2.9 %MVC), whereas in the LBB they were highest in the supinated position (8.6 +/- 2.0 %MVC). Motor unit discharge rates of the LBB did not change with forearm position. In the SBB, MUDRs were highest when the forearm was supinated, and also greater when compared with the LBB in this position. No position-dependent changes were observed for MU discharge variability in the LBB, but the SBB exhibited greatest MU discharge variability in the pronated position. The results suggest that MU activity is modulated following a change in forearm position, but the response is similar in young and old adults.

Inter-rater reliability of motor unit number estimates and quantitative motor unit analysis in the tibialis anterior muscle.

OBJECTIVE: To establish the inter-rater reliability of decomposition-based quantitative electromyography (DQEMG) derived motor unit number estimates (MUNEs) and quantitative motor unit (MU) analysis. METHODS: Using DQEMG, two examiners independently obtained a sample of needle and surface-detected motor unit potentials (MUPs) from the tibialis anterior muscle from 10 subjects. Coupled with a maximal M wave, surface-detected MUPs were used to derive a MUNE for each subject and each examiner. Additionally, size-related parameters of the individual MUs were obtained following quantitative MUP analysis. RESULTS: Test-retest MUNE values were similar with high reliability observed between examiners (ICC=0.87). Additionally, MUNE variability from test-retest as quantified by a 95% confidence interval was relatively low (+/-28 MUs). Lastly, quantitative data pertaining to MU size, complexity and firing rate were similar between examiners. CONCLUSION: MUNEs and quantitative MU data can be obtained with high reliability by two independent examiners using DQEMG. SIGNIFICANCE: Establishing the inter-rater reliability of MUNEs and quantitative MU analysis using DQEMG is central to the clinical applicability of the technique. In addition to assessing response to treatments over time, multiple clinicians may be involved in the longitudinal assessment of the MU pool of individuals with disorders of the central or peripheral nervous system.

Age- and sex-related differences in muscle activation for a discrete functional task.

Electromyography (EMG) recordings for a typical 8-h day have indicated that burst activity is greater in old adults compared with young adults; these age-related adaptations might be due to the tasks undertaken. The purpose of the present study was to determine whether EMG burst activity differs between young and old men and women for a discrete task of daily living, and to assess whether the time of day when the task is performed influences the EMG burst patterns. Subjects completed a discrete functional task of a grocery bag carry prior to and following 8 h of daily activity. Surface EMG was recorded from the biceps brachii, triceps brachii, vastus lateralis, and biceps femoris. Spatial and temporal characteristics of the bursts were quantified as a period of EMG activity being greater than 2% maximum EMG and for a duration longer than 0.1 s. Burst activity did not differ between the morning and evening recordings, which indicate that the time of day does not influence burst activity recorded for a discrete task. Although there were no differences in burst number between young (10.9 +/- 1.0) and old (11.4 +/- 0.7) adults, burst duration and area were 3-7 times larger in old adults compared with young adults. The number of bursts in women (7.9 +/- 1.0) were ~85% less compared with men (14.6 +/- 0.7), but burst duration and burst area were approximately three times larger in women compared with men. Thus, older adults demonstrate higher levels of burst activity compared with young adults, and these age-related changes in burst activity are augmented in women.

Quality of life and acceptability of medical versus surgical management of early pregnancy failure.

OBJECTIVE: This study compares quality of life (QOL) and acceptability of medical versus surgical treatment of early pregnancy failure (EPF). DESIGN: A randomised clinical trial of treatment for EPF compared misoprostol vaginally versus vacuum aspiration (VA). SETTING: A multisite trial at four US Urban University Hospitals. POPULATION: A total of 652 women with an EPF were randomised to treatment. METHODS: Participants completed a daily symptom diary and a questionnaire 2 weeks after treatment. MAIN OUTCOME MEASURES: The questionnaire assessment included subscales of the Short Form-36 Health Survey Revised for QOL and measures of wellbeing, recovery difficulties, and treatment acceptability. RESULTS: The two groups did not differ in mean scores for QOL except bodily pain; medical treatment was associated with higher levels of bodily pain than VA (P < 0.001). Success of treatment was not related to QOL, but acceptability of the procedure was decreased for medical therapy if unsuccessful (P = 0.003). Type of treatment was not associated with differences in recovery, and the two groups reported similar acceptability except for cramping (P = 0.02), bleeding (P < 0.001), and symptom duration (P = 0.03). CONCLUSIONS: Despite reporting greater pain and lower acceptability of treatment-related symptoms, QOL and treatment acceptability were similar for medical and surgical treatment of EPF. Acceptability, but not QOL, was influenced by success or failure of medical management.

Endometrial thickness after misoprostol use for early pregnancy failure.

OBJECTIVES: To assess if there was any potential relationship between endometrial thickness and final treatment outcome in women successfully treated with misoprostol for a first trimester anembryonic gestation, embryonic demise or fetal demise. METHODS: Eighty women were treated with up to two doses of misoprostol 800 microg vaginally for early pregnancy failure. Subjects were scheduled to return 2 (range 1-4), 7 (range 5-9) and 14 (range 12-17) days after treatment. Transvaginal ultrasonography was performed at each follow-up visit. RESULTS: The median endometrial thickness at each of the follow-up visits for women who had expelled the gestational sac was 14 mm, 10 mm, and 7 mm, respectively. The endometrial thickness at the first follow-up visit exceeded 15 mm in 20 subjects (36%) and 30 mm in four subjects (7%). Only three women had a suction aspiration for bleeding after documented expulsion. The endometrial thickness for these women was 11, 13, and 14 mm at the first follow-up visit. CONCLUSIONS: There is no obvious relationship between increasing endometrial thickness and the need for surgical intervention in women treated with misoprostol for early pregnancy failure.

An ultrastructural investigation of the 'microsclerotia' formed in single cells of root cortical cells associated with corky root rot of tomato.

White and Scott (1973) described two forms of microsclerotia associated with corky root rot of tomato, one being formed in single cells of the outer root cortical cells and the other produced in culture from isolation of diseased roots and in degenerated root debris. By assuming that both forms were of fungal origin, they conducted an ultrastructural study using the microsclerotia produced in culture but not those formed in single cells. They demonstrated that the microsclerotia from culture consisted of hardened, interwoven hyphae of the fungus, Pyrenochaeta lycopersici. Since there have been doubts about the nature of the microsclerotia formed in single cells, an ultrastructural study was conducted. The results demonstrated clearly that the 'microsclerotia' formed in single cells of the root cortical cells were not composed of fungal mycelia, indeed these blackened cells or 'microsclerotia' were filled with numerous crystallines. There was no evidence of the presence of fungal hyphae in or around these cells. Both diseased and healthy, and young and old root cortex cells of many cultivars of tomato contained cells filled with crystallines. Therefore, it is clear that the 'microsclerotia' formed in single cells of the outer cortex described by White and Scott are not microsclerotia of the fungus, P. lycopersici.

Contraceptive vaginal rings.

Contraceptive vaginal rings (CVRs) contain sex steroids that diffuse through a plastic polymer ring at a constant rate and are absorbed directly through the vaginal epithelium into the systemic circulation. This delivery system provides many advantages over oral contraceptives (OCs), including avoidance of the first-pass effect through the liver, constant serum steroid levels, longer duration of use, and greater bioavailability of the hormones. CVRs containing progestin only are designed for continuous use for 3 to 6 months. Those containing progesterone alone are indicated for use in women who are breastfeeding. Large clinical trials of progestin-containing CVRs demonstrated good efficacy and safety of the CVR, with continuation rates similar to that of OCs. CVRs containing a combination of estrogen and progestin are designed to be used for 1 to 12 months in a cyclic manner similar to OCs, with withdrawal bleeding in the fourth week of each cycle. In clinical trials these CVRs have typical use efficacies similar to OCs, with an acceptable pattern of bleeding.

Early pregnancy termination with vaginal misoprostol combined with loperamide and acetaminophen prophylaxis.

The objectives of this prospective non-concurrent cohort study were to confirm the efficacy of vaginal misoprostol for early pregnancy termination and to determine whether the incidence of side effects is lower with prophylactic loperamide and acetaminophen. Two-hundred women with an intrauterine pregnancy < or =56 days gestational age seeking medical pregnancy termination in an ambulatory research clinic were enrolled in the study. One-hundred participants (group 1) ingested 4 mg of loperamide and 500 mg of acetaminophen before the vaginal placement of 800 mirog of misoprostol moistened with 2 mL of saline. If abortion had not occurred, the same regimen was repeated every 24 h (maximum three doses). One-hundred participants (group 2) from the same clinic who previously underwent the same misoprostol regimen without prophylactic medication served as a control group for comparison with respect to abortion success and the incidence of side effects. The rate of successful abortion was not statistically significantly different between the two groups (group 1 93%, group 2 89%). The incidence of opiate analgesic use was significantly less in group 1 (4%) compared with group 2 (16%) (OR 0.22, 95% CI 0.06-0.73, p = 0.01). There was a significantly lower incidence of diarrhea in group 1 (23%) compared with group 2 (44%) (OR 0.38, 95% CI 0.20-0.73, p = 0.003). There was no difference in the incidence of fever/chills or the incidence of emesis between the two groups. Vaginal misoprostol is effective for termination of pregnancy < or = 56 days and the incidence of diarrhea and the use of opiate analgesia is significantly reduced with prophylactic loperamide and acetaminophen.