Acute Effects of 3 Neuromuscular Electrical Stimulation Waveforms on Exercising and Recovery Microvascular Oxygenation Responses.

CONTEXT: When emphasizing muscular strength during postoperative rehabilitation it is recommended to use a neuromuscular electrical stimulation (NMES) waveform that elicits the greatest muscle force and local metabolic demand that is also well tolerated. The present investigation examined the effects that 3 different clinically used NMES waveforms had on the electrically elicited force (EEF), local metabolic demand (exercising muscle oxygen saturation [SmO2]), and the subsequent reactive hyperemia response (recovery total hemoglobin concentration [THb]) of the knee extensors. DESIGN: Single session repeated-measures design. METHODS: EEF, local metabolic demand, and reactive hyperemia responses were measured during and subsequent to 3 NMES waveforms: Russian burst modulated alternating current (RUS), biphasic pulsed current (VMS™), and burst modulated biphasic pulsed current (VMS-Burst™). Exercising SmO2 and recovery THb were assessed noninvasively using a near-infrared spectroscopy sensor placed on the vastus lateralis. Participants completed one set of 10 repetitions of each NMES waveform and were provided with 5 minutes of passive, interset recovery. Two-way, repeated-measures analysis of variance examined if NMES waveform or repetition significantly affected (P < .05) EEF or exercising SmO2. Two-way, repeated-measures analysis of variance examined if NMES waveform or recovery time affected recovery THb. RESULTS: VMS™ and VMS-Burst™ yielded higher EEF (F = 11.839, P < .001) and greater local metabolic stress (lower exercising SmO2, F = 13.654, P < .001) compared with RUS. Greater rate of EEF decline throughout the NMES set was observed during RUS (%Δ = -50 [6] %Rep1) compared with VMS-Burst™ (%Δ = -30 [7] %Rep1) and VMS™ (%Δ = -32 [7] %Rep1). VMS™ elicited a higher reactive hyperemia response (higher recovery THb) compared with RUS (F = 3.427, P = .048). CONCLUSIONS: The present findings support the use of VMS™ or VMS-Burst™ compared with RUS when promoting muscular strength. In addition, the use of VMS™ might provide a greater blood volume to the target muscle subsequent to NMES contractions compared with RUS.

Changes in microvascular oxygenation and total hemoglobin concentration of the vastus lateralis during neuromuscular electrical stimulation (NMES).

Background and Introduction: Neuromuscular electrical stimulation (NMES) is predicated on eliciting muscle contractions and increasing muscle demand to promote increase in strength. Previous studies have shown differences in the magnitude of elicited force among various NMES waveforms but less is known about metabolic demand of muscle during NMES.Objective/Purpose: The purpose of this study was to compare elicited force and muscle metabolic demand during electrically elicited contractions using different NMES waveforms.Methods: A single-session repeated measures design was used. Electrically elicited force (EEF), microvascular oxygenation (SmO2), total hemoglobin concentration ([THC]) of the vastus lateralis, and subject tolerance (VAS score) were measured using three NMES waveforms; burst modulated alternating current (Russian), biphasic pulsed current (VMS®), and burst modulated biphasic pulsed current (VMS-burst®).Results: A significant main effect for waveform was noted for EEF (F = 12.693, p < .001), SmO2 (F = 8.340, p = .001), and VAS (F = 4.213, p = .025), but not [THC]. Compared to Russian current, VMS-burst and VMS resulted in significantly greater EEF (p = .001; p = .009) and local metabolic demand (i.e. decreased SmO2) (p = .005; p = .003), but not [THC]. VAS was significantly greater (p = .023) for VMS (4.2) compared to Russian (3.07) but not different between VMS-burst and Russian and VMS-burst and VMS.Conclusion: Greater muscle force and local metabolic demand were observed with VMS-burst and VMS compared to Russian current. These data provide novel evidence to guide clinical decision making when selecting an NMES waveform.

Efficiency of neuromuscular electrical stimulation: A comparison of elicited force and subject tolerance using three electrical waveforms.

OBJECTIVE: Efficacy of neuromuscular electrical stimulation (NMES) is limited by the discomfort of electrically elicited contractions. Most studies of tolerance to NMES have examined stimulation to maximal tolerance. NMES efficiency is the amount of elicited force at a specific level of tolerance. This study is the first to describe and examine such. DESIGN: A repeated measures design was used. Electrically elicited force (EEF) was measured using three waveforms: burst-modulated alternating current (BMAC), pulsed current (PC), and burst-modulated pulsed current (BMPC). EEF at a tolerance rating of 5/10 on a visual analog scale (VAS) was recorded. The dependent variables were EEF up to 5/10 VAS, current amplitude at 5/10, and percent maximal isometric force at 5/10. RESULTS: EEF and percent maximal voluntary isometric force were significantly greater with BMPC versus BMAC (p = 0.001 and 0.004). No differences were noted between PC and BMAC or BMPC and PC. Amplitude was significantly greater with BMAC compared to BMPC and PC (p = 0.003 and 0.015). No difference in amplitude was noted between PC and BMPC. CONCLUSION: For the same level of discomfort, BMPC yielded one-third greater muscle force than BMAC and at a lesser current amplitude. These data evidence a greater efficiency for BMPC than BMAC.

Muscle force production with low and medium frequency burst modulated biphasic pulsed currents.

OBJECTIVE: Russian current, a medium frequency burst modulated alternating current (BMAC), is widely used for NMES, but has not been shown to elicit forces near voluntary maximum. In contrast, low frequency BMAC has been shown to produce greater force production than Russian and most recently, medium frequency burst modulated biphasic pulsed current (BMBPC) elicited greater force than Russian. Whether low frequency BMBPC yields greater force than medium frequency BMBPC is unknown. This study examined elicited forces using BMBPC with low and medium frequency carrier currents. DESIGN: A cross-over design where percent maximal isometric knee extensor forces (%MVIF) elicited using BMBPC with low or medium kilohertz carrier frequencies were compared in 23 subjects. Perceived discomfort was also assessed. Data were compared using paired samples t-tests. RESULTS: 98.4% of the MVIF was elicited with the low frequency BMBPC which was significantly greater (p < 0.001) than the 40.4% yielded by the medium frequency current. Cohen's d effect size of 2.146 indicated a "huge effect". Perceived discomfort of the low frequency current was 5.7/10 and was significantly greater (p < 0.001) than the medium frequency current (3.6/10). CONCLUSION: BMBPC with low frequency carrier current elicits forces approximating maximal volitional force. These findings offer new evidence with strong clinical implications when using NMES.

Interferential and burst-modulated biphasic pulsed currents yield greater muscular force than Russian current.

OBJECTIVE: Previous data regarding neuromuscular electrical stimulation (NMES) have suggested that muscle torque production with interferential current (IFC) is inferior to Russian current; however, waveform parameters specific and critical to NMES were inconsistent, making interpretation of previous findings precarious. The purpose of this investigation was to compare muscle force production of three electrical stimulating waveforms when using equivalent stimulus parameters. DESIGN: The percent of maximal voluntary isometric knee extensor force (%MVIF) elicited using interferential, Russian, and burst-modulated biphasic pulsed currents were compared in 23 healthy college-aged subjects. A repeated measures single factor design in a university laboratory setting was used. RESULTS: A significant effect for waveform used was noted. Data showed significantly greater %MVIF of the knee extensors were obtained using IFC or burst-modulated BP current versus conventional Russian current. CONCLUSIONS: The results of this investigation suggest that IFC and burst-modulated BP current are viable waveform options for purposes of eliciting muscle force. These findings offer significant new evidence with strong clinical implications when selecting waveform parameters for elicitation of muscle force for NMES.

Facilitating activation of the peroneus longus: electromyographic analysis of exercises consistent with biomechanical function.

Exercises for the ankle are often used to improve sport performance through balance and stability or to prevent or recover from ankle injury. Ankle training programs often include exercises for the primary muscle of the lateral ankle, the peroneus longus (PL). However, many exercises for the PL are non-weight bearing and unidirectional. However, data from biomechanical studies show that peak activity of the PL occurs neither in non-weight-bearing nor during uniplanar movements. This lack of congruency may limit the effectiveness of PL training. Exercises more consistent with the biomechanical function of the PL may increase the efficacy of ankle training. This study examined and compared the electromyographic (EMG) activity of the PL during 2 exercises that specifically address the known biomechanical function of the PL and a traditional non-weight-bearing unidirectional PL exercise. Twenty healthy college-aged men and women (age 24.8 +/- 2.7 years) without history of ankle injury were examined in a single-session repeated measures design. The average root means square (RMS) values of the PL during each of the 3 exercises were measured and compared to assess for differences in magnitude of muscular activity. The RMS activity of the PL was significantly greater (p < 0.05) in each of the biomechanically correct exercises when compared with the conventional exercise. However, no significant difference was noted in EMG activity between the 2 biomechanical exercises. This study provides evidence for increased activity from the PL during 2 exercises that more accurately reflect its biomechanical function. Use of these exercises when training the PL for sports performance or rehabilitation may increase the effectiveness of ankle training programs that include PL activity.

Effect of acute fatigue of the hip abductors on control of balance in young and older women.

OBJECTIVE: To examine the effects of acute fatigue of the hip abductors on the control of balance in young and older women. DESIGN: Pretest-posttest. SETTING: University research laboratory. PARTICIPANTS: Healthy young women (n=20; age, 23.0+/-1.5y; height, 166.52+/-4.5 cm; mass, 65.33+/-10.5 kg) and community-dwelling older women (n=20; age, 71.65+/-7.2y; height, 162.31+/-3.8 cm; mass, 71.16+/-11.6 kg) without a fall history. INTERVENTION: Measurements of control of single-limb balance before and after fatiguing the hip abductors of the dominant leg. MAIN OUTCOME MEASURE: Performance on 3 clinical assessments of control of balance: the modified Functional Reach Test in the forward, left, and right directions; the Lower-Extremity Reach Test in forward and lateral directions; and the Single-Limb Stance Time Test (SLSTT). RESULTS: Although the younger subjects showed a significantly greater control of balance than the older women in most tests, control of balance after acute fatigue failed to show a significant decline in either age group. The only exception to this was the SLSTT in the younger women in whom a significant 26% decline was noted (P<.05). CONCLUSIONS: Acute fatigue of the hip abductors did not result in a decreased control of balance in healthy young or older women without fall history. Despite considerable changes in movement strategies used to complete the postfatigue tests of balance, quantitative measures of balance did not decrease.

Control of balance differs after knee or ankle fatigue in older women.

OBJECTIVE: To examine the effects of acute isokinetic knee or ankle fatigue on control of static and dynamic balance in older women. DESIGN: Pretest and posttest. SETTING: University research laboratory. PARTICIPANTS: Eighteen healthy, community-dwelling older women (age, 77 +/- 6 y) with no history of falling. INTERVENTIONS: Measurements of static and dynamic balance control before and after isokinetically fatiguing the ankle plantar- and dorsiflexors or knee extensors and flexors in separate sessions. MAIN OUTCOME MEASURES: Performance on 3 clinical assessments of control of balance: modified Functional Reach Test (mFRT), Lower-Extremity Reach Test (LERT), and Single-Limb Stance Time Test (SLSTT). RESULTS: Balance declined in the mFRT after fatigue to each joint, with no significant difference in the magnitude of change between joints. Control of balance during the LERT decreased significantly only after knee fatigue, and control of balance during the SLSTT was significantly reduced only after ankle fatigue. CONCLUSIONS: Balance performance after acute isokinetic muscular fatigue to the knee or ankle is specific to the muscle groups fatigued and the balance tests used.

A comparison of bone mineral density in adolescent female swimmers, soccer players, and weight lifters.

PURPOSE: The study was designed to examine the effect of sports of varying skeletal loading on bone density in adolescent female athletes. METHODS: Bone mineral densities of female swimmers, soccer players, and weight lifters were examined. Between-sport comparisons were made using a one-way analysis of covariance with age and body mass index as covariates and group bone mass density (BMD) was compared to the World Health Organization's (WHO) normative values for adult females. RESULTS: BMD was significantly greater in the soccer group compared to the weight lifting (p = 0.025) and swimming groups (p = 0.001) with no difference between weight-lifting and swimming groups (p = 0.209). Compared to normative data from the WHO, soccer was the only sport whose participants' BMDs were significantly greater than adult norms (p = 0.003), while those of the swimmers were significantly less (p < 0.001) than adult females, and the weight lifters were not different (p = 0.103). CONCLUSIONS: Participation in sports such as soccer or weight lifting with significant skeletal loading may enhance BMD in adolescent females.

Effects of a short-term dynamic balance training program in healthy older women.

PURPOSE: Aging is associated with deterioration of the physiologic systems controlling balance. Consequently, a multitude of intervention trials has appeared in the last 2 decades attempting to improve control of balance. Effective programs often require substantial and frequent time commitments, expensive and specialized equipment, professional assistance, and clinical settings. This investigation reports the effects of a simple, short-term balance training program on dynamic balance in healthy older women. METHODS: Subjects included 11 healthy women (75.6+/-6.4 years) who participated in biweekly, 15-minute balance training sessions for 5 weeks, and 10 age-matched women (71.2+/-9.1 years) who served as controls. Balance training involved medial-lateral and anterior-posterior movements and bilateral partial squats while standing on semi-compressible foam roller-devices. Dynamic balance was quantified using functional reach in the forward, left, and right directions, and a lower extremity reach test. RESULTS: Significant increases were observed in the balance trained group: 25% in functional reach right (P=0.014) and left (P<0.001) and 16% in lower extremity reach (P=0.001). No change was noted in the control group. CONCLUSIONS: Improvements in dynamic balance can be realized following 5 weeks of dynamic balance training using this novel, simplistic, and short-term protocol.

A comparison of 3 hand-held dynamometers used to measure hip abduction strength.

Quantification of strength with hand-held dynamometers is commonplace. Hand-held dynamometers offer ease of use; however, previous investigations have shown much variability between repeated measures using the same dynamometer. Even less is known regarding the degree of variability between various dynamometers. Therefore, the intent of this investigation was to compare measures of hip abduction strength recorded with 3 different but commonly used hand-held dynamometers, specifically the Microfet 2 Load Cell, Jamar Hand-Held, and Dial Push-Pull Gauge. Maximal isometric hip abduction strength was recorded in 10 women (27.6 +/- 6.2 years) over 3 consecutive days using a different device each day. A significant difference in recorded force was noted between the devices (p < 0.001) as the Microfet showed significantly less force than the others. This was supported by intraclass correlation coefficients (ICCs) ranging from 0.277 to 0.688. These data suggest that consideration must be given to using the same dynamometer when quantifying strength over repeated sessions.

The initial effects of low-volume strength training on balance in untrained older men and women.

Evidence indicates that leg weakness in older adults is associated with decreased control of balance. The gender-specific implications of strength training on control of balance in older men and women remains unknown. This study examined the initial adaptations to 12 weeks of low-volume, single-set-to-failure strength training and its effect on quadriceps strength and control of multidirectional balance in previously untrained older men (n = 11) and women (n = 11) 59-83 years of age. Leg strength increased 23-30% (p < 0.001) across genders; however, the effect on balance varied between genders. No significant changes were noted in the women, whereas 37% (p < 0.014) more sway in the medial-lateral direction was noted in the men, with no change in the anterior-posterior direction. These results demonstrate that this training protocol may not be effective for improving balance and may lead to worsening of balance in older men.