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William Holcomb, Mack D. Rubley and Tedd J. Girouard

Context:

Electrical stimulation using simultaneous application of two current types for multiple effects is a current treatment option, but the effect of this treatment is not currently known.

Objectives:

To compare isometric knee extension torque when using neuromuscular electrical stimulation (NMES) in combination with High Voltage Pulsed Current (HVPC) versus NMES alone during three contraction conditions of quadriceps.

Design:

Counterbalanced, within-subjects design to test independent variables, stimulation protocol, and contraction condition; ANOVA to analyze dependent variable, peak torque.

Setting:

Athletic Training Research Laboratory. Participants: 14 healthy subjects (7 male and 7 female, age = 21.9 ± 2.0 yr, height = 173.4 ± 10.1cm, weight = 76.1 ± 16.7 kg).

Intervention:

Participants performed three contraction conditions during two stimulation protocols.

Main Outcome Measure:

Peak isometric knee extension torque.

Results:

The main effect for Stimulation Protocol was not significant: F1,26 = .01, P = .94.

Conclusion:

Simultaneous application of HVPC with NMES does not facilitate the neuromuscular response but may provide an efficient treatment when managing atrophy, strength loss, pain, and edema associated with reconstructive surgery.

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William R. Holcomb, Shahin Golestani and Shante Hill

Context:

Neuromuscular electrical stimulation (NMES) can be used to prevent the atrophy and strength loss associated with immobilization.

Objective:

To compare the effects of biphasic current and the modulated “Russian” current on muscular torque production during different contraction conditions.

Design, Setting, and Participants:

In a within-subjects design, 10 healthy subjects in an athletic training laboratory received NMES.

Interventions:

Isometric knee-extension torque was recorded with the Biodex™ under 4 conditions: maximum voluntary contraction (MVC; control), MVC superimposed with low-intensity stimulation (sham), MVC superimposed with high-intensity stimulation, and high-intensity stimulation only.

Main Outcome Measure:

Data normalized for body weight were analyzed using a 2 (current type) X 4 (condition) repeated-measures analysis of variance.

Results:

The main effect for current type was not significant, F1,9 = .03, P = .87.

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William R. Holcomb, Mack D. Rubley, Michael G. Miller and Tedd J. Girouard

Context:

Previous studies using neuromuscular electrical stimulation (NMES) have suggested that 30-second rest intervals are too short for sufficient recovery.

Objective:

To compare the effect of rest interval on knee-extension torque production.

Design:

Counterbalanced mixed design to test independent variable, rest interval; ANOVA to analyze dependent variable, percentage decline.

Setting:

Athletic training research laboratory.

Participants:

24 healthy men and women.

Intervention:

Participants performed knee extension under 2 contraction conditions, maximum voluntary isometric contraction (MVIC) and NMES with either 30- or 120-second rest between repetitions.

Main Outcome Measure:

Peak torque produced during each repetition of a 5-repetition set.

Results:

The main effect for rest interval was significant (F 1,23 = 30.30, P = .001), as was the main effect for condition (F 1,23 = 11.18, P = .003).

Conclusions:

A 120-second rest between repetitions is recommended when using NMES in early rehabilitation because force decline across repetitions with 30-second rest during NMES is greater than with MVIC.

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Hui Ying Wu, Jui Hung Tu, Chin Hsing Hsu and Te Hung Tsao

The effect of low-impact dance on blood metabolites, the joint range of motion (ROM) of the lower extremities, knee extension torque, bone mass density (BMD), the number of falls, and the confidence to perform daily activities (Modified Falls Efficacy Scale [MFES]) was examined in older sedentary women (age: 59 ± 4 years) before and after a 16-week intervention. Results showed that the average score for the MFES, some parameters of blood chemistry, and joint ROM were significantly improved after low-impact intervention. In addition to improvements in blood lipids and body fat percentages, the increases shown in the parameters regarding the lower extremities may contribute to confidence in performing common daily activities in older women, although the number of falls did not significantly differ between the two groups during the 16-week period.

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Brandon Warner, Kyung-Min Kim, Joseph M. Hart and Susan Saliba

Context:

Quadriceps function improves after application of focal joint cooling or transcutaneous electrical nerve stimulation to the knee in patients with arthrogenic muscle inhibition (AMI), yet it is not known whether superficial heat is able to produce a similar effect.

Objective:

To determine quadriceps function after superficial heat to the knee joint in individuals with AMI.

Design:

Single blinded randomized crossover.

Setting:

Laboratory.

Patients:

12 subjects (4 female, 8 males; 25.6 ± 7.7 y, 177.2 ± 12.7 cm, 78.4 ± 18.2 kg) with a history of knee-joint pathology and AMI, determined with a quadriceps central activation ratio (CAR) of <90%.

Intervention:

3 treatment conditions for 15 min on separate days: superficial heat using a cervical moist-heat pack (77°C), sham using a cervical moist pack (room temperature at about 24°C), and control (no treatment). All subjects received all treatment conditions in a randomized order.

Main Outcome Measures:

Central activation ratio and knee-extension torque during maximal voluntary isometric contraction with the knee flexed to 60° were collected at pre, immediately post, 30 min post, and 45 min posttreatment. Skin temperature of the quadriceps and knee and room temperature were also recorded at the same time points.

Results:

Three (treatment conditions) by 4 (time) repeated ANOVAs found that there were no significant interactions or main effects in either CAR or knee-extension torque (all P > .05). Skin-temperature 1-way ANOVAs revealed that the skin temperature in the knee during superficial heat was significantly higher than other treatment conditions at all time points (P < .05).

Conclusions:

Superficial heat to the knee joint using a cervical moist-heat pack did not influence quadriceps function in individuals with AMI in the quadriceps.

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Christopher Kuenze, Jay Hertel, Susan Saliba, David R. Diduch, Arthur Weltman and Joseph M. Hart

Context:

Normal, symmetrical quadriceps strength is a common clinical goal after anterior cruciate ligament reconstruction (ACLR). Currently, the clinical thresholds for acceptable unilateral quadriceps function and symmetry associated with positive outcomes after return to activity are unclear.

Objective:

To establish quadriceps-activation and knee-extension-torque cutoffs for clinical assessment after return to activity after ACLR.

Design:

Descriptive laboratory study.

Setting:

Laboratory.

Patients:

22 (10 female, 12 male; age = 22.5 ± 5.0 y, height = 172.9 ± 7.1 cm, mass = 74.1 ± 15.5 kg, months since surgery = 31.5 ± 23.5) recreationally active persons with a history of unilateral, primary ACLR at least 6 months prior and 24 (12 female/12 male, age = 21.7 ± 3.6 y, height = 168.0 ± 8.8 cm, mass = 69.3 ± 13.6 kg) recreationally active healthy participants.

Main Outcome Measures:

Patient-reported measures of pain, knee-related function, and physical activity level were recorded for all participants. Normalized knee-extension maximum-voluntary-isometric-contraction (MVIC) torque (Nm/kg) and quadriceps central-activation ratio (CAR, %) were measured bilaterally in all participants. Receiver-operator-characteristic (ROC) curves were used to establish thresholds for unilateral measures of normalized knee-extension MVIC torque and quadriceps CAR, as well as limb-symmetry indices (LSI). ROC curves then established clinical thresholds for normalized knee-extension MVIC torque and quadriceps CAR LSIs associated with healthy knee-related function.

Results:

Involved-quadriceps CAR above 89.3% was the strongest unilateral indicator of healthy-group membership, while quadriceps CAR LSI above 0.996 and knee-extension MVIC torque above 0.940 were the strongest overall indicators. Unilateral normalized knee-extension MVIC torque above 3.00 Nm/kg and quadriceps CAR LSI above 0.992 were the best indicators of good patient-reported knee-related outcomes.

Conclusions:

Threshold values established in this study may provide a guide for clinicians when making return-to-activity decisions after ACLR. Normalized knee-extension MVIC torque (>3.00 Nm/kg) and quadriceps CAR symmetry (>99.6%) are both strong indicators of good patient-reported outcomes after ACLR.

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Ian J. Dempsey, Grant E. Norte, Matthew Hall, John Goetschius, Lindsay V. Slater, Jourdan M. Cancienne, Brian C. Werner, David R. Diduch and Joseph M. Hart

. The frequency, or days of PT completed per week, yielded a weak, positive correlation with peak isokinetic knee extension torque ( r  = .290, P  = .03). No additional correlations were observed ( P  > .05). Table 3 Relationship Between Physical Therapy and Patient Outcomes Correlation coefficient, r

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Christopher Kuenze, Jay Hertel and Joseph M. Hart

Purpose:

Persistent quadriceps weakness due to arthrogenic muscle inhibition (AMI) has been reported after anterior cruciate ligament (ACL) reconstruction. Fatiguing exercise has been shown to alter lower extremity muscle function and gait mechanics, which may be related to injury risk. The effects of exercise on lower extremity function in the presence of AMI are not currently understood. The purpose of this study was to compare the effect of 30 min of exercise on quadriceps muscle function and soleus motoneuron-pool excitability in ACL-reconstructed participants and healthy controls.

Methods:

Twenty-six (13 women, 13 men) healthy and 26 (13 women, 13 men) ACL-reconstructed recreationally active volunteers were recruited for a case-control laboratory study. All participants completed 30 min of continuous exercise including alternating cycles of inclined-treadmill walking and bouts of squats and step-ups. Knee-extension torque, quadriceps central activation ratio (CAR), soleus H:M ratio, and soleus V:M ratio were measured before and after 30 min of exercise.

Results:

There was a significant group × time interaction for knee-extension torque (P = .002), quadriceps CAR (P = .03), and soleus V:M ratio (P = .03). The effect of exercise was smaller for the ACL-R group than for matched controls for knee-extension torque (ACL-R: %Δ = −4.2 [−8.7, 0.3]; healthy: %Δ = −14.2 [−18.2, −10.2]), quadriceps CAR (ACL-R: %Δ = −5.1 [−8.0, −2.1]; healthy: %Δ = −10.0 [−13.3, −6.7]), and soleus V:M ratio (ACL-R: %Δ = 37.6 [2.1, 73.0]; healthy: %Δ = −24.9 [−38.6, −11.3]).

Conclusion:

Declines in quadriceps and soleus volitional muscle function were of lower magnitude in ACL-R subjects than in healthy matched controls. This response suggests an adaptation experienced by patients with quadriceps AMI that may act to maintain lower extremity function during prolonged exercise.

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Scott J. Black, Michael L. Woodhouse, Stephen Suttmiller and Larry Shall

The effects of hip position on thigh electromyographic (EMG) activity and knee torque were evaluated. Twenty-four recreational athletes (12 males and 12 females) volunteered to participate. Subjects were tested isokinetically at 30°/s in sitting and supine positions both concentrically and eccentrically during knee flexion and extension. Gravity-corrected torques (N·m) were obtained for all tests. EMG amplitude (mV) was collected via surface electrodes. Torque values were significantly greater (p<.05) for knee flexion in the sitting position when compared to the supine. EMG activity did not change relative to hip position but typically increased (p<.05) during concentric trials. Knee extension torque and EMG activity did not change during sitting or supine positions. Results indicated that the sitting position had statistically significant advantages over the supine position for producing greater hamstring torque and maintaining similar levels of EMG output during isokinetic knee flexion.

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Ashley Stern, Chris Kuenze, Daniel Herman, Lindsay D. Sauer and Joseph M. Hart

Context:

Central and peripheral muscle fatigue during exercise may exacerbate neuromuscular factors that increase risk for noncontact anterior cruciate ligament injury.

Objective:

To compare lower extremity motor-evoked potentials (MEPs), muscle strength, and electromyography (EMG) activation after an exercise protocol.

Design:

Pretest, posttest group comparison.

Setting:

University laboratory.

Participants:

34 healthy volunteers (17 female, age = 21.9 ± 2.3 years, weight = 77.8 ± 3.0 kg, height = 171.1 ± 6.6 cm, and 17 male, age = 23.4 ± 6.5 years, weight = 81.6 ± 3.3 kg, height = 179.6 ± 7.3 cm).

Intervention:

A standardized 30-min exercise protocol that involved 5 repeated cycles of uphill walking, body-weight squatting, and step-ups.

Main Outcome Measures:

Quadriceps and hamstring MEP amplitude (mV) and transmission velocity normalized to subject height (m/s) were elicited via transcranial magnetic stimulation and measured via surface EMG. Quadriceps and hamstring peak EMG activation (% MVIC) and peak torque (Nm/kg) were measured during MVICs. Separate ANCOVAs were used to compare groups after exercise while controlling for baseline measurement.

Results:

At baseline, males exhibited significantly greater knee-extension torques (males = 2.47 ± 0.68 Nm/kg, females = 1.95 ± 0.53 Nm/kg; P = .036) and significantly higher hamstring MEP amplitudes (males = 223.5 ± 134.0 mV, females = 89.3 ± 77.6 mV; P = .007). Males exhibited greater quadriceps MEP amplitude after exercise than females (males = 127.2 ± 112.7 mV, females = 32.3 ± 34.9 mV; P = .016).

Conclusions:

Males experienced greater peripheral neuromuscular changes manifested as more pronounced reductions in quadriceps torque after exercise. Females experienced greater central neuromuscular changes manifested as more pronounced reduction in quadriceps MEP amplitude. Reduced central neural drive of the quadriceps coupled with knee-extension torque preservation after exercise may increase risk of knee injury in females.