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Mark A. Sutherlin and Joseph M. Hart

Context:

Individuals with a history of low back pain (LBP) may present with decreased hip-abduction strength and increased trunk or gluteus maximus (GMax) fatigability. However, the effect of hip-abduction exercise on hip-muscle function has not been previously reported.

Objective:

To compare hip-abduction torque and muscle activation of the hip, thigh, and trunk between individuals with and without a history of LBP during repeated bouts of side-lying hip-abduction exercise.

Design:

Repeated measures.

Setting:

Clinical laboratory.

Participants:

12 individuals with a history of LBP and 12 controls.

Intervention:

Repeated 30-s hip-abduction contractions.

Main Outcome Measures:

Hip-abduction torque, normalized root-mean-squared (RMS) muscle activation, percent RMS muscle activation, and forward general linear regression.

Results:

Hip-abduction torque reduced in all participants as a result of exercise (1.57 ± 0.36 Nm/kg, 1.12 ± 0.36 Nm/kg; P < .001), but there were no group differences (F = 0.129, P = .723) or group-by-time interactions (F = 1.098, P = .358). All participants had increased GMax activation during the first bout of exercise (0.96 ± 1.00, 1.18 ± 1.03; P = .038). Individuals with a history of LBP had significantly greater GMax activation at multiple points during repeated exercise (P < .05) and a significantly lower percent of muscle activation for the GMax (P = .050) at the start of the third bout of exercise and for the biceps femoris (P = .039) at the end of exercise. The gluteal muscles best predicted hip-abduction torque in controls, while no consistent muscles were identified for individuals with a history of LBP.

Conclusions:

Hip-abduction torque decreased in all individuals after hip-abduction exercise, although individuals with a history of LBP had increased GMax activation during exercise. Gluteal muscle activity explained hip-abduction torque in healthy individuals but not in those with a history of LBP. Alterations in hip-muscle function may exist in individuals with a history of LBP.

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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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Luke Donovan, Joseph M. Hart and Jay Hertel

Context:

Ankle-destabilization devices are rehabilitation tools that may improve neuromuscular control by increasing lower-extremity muscle activation. Their effects should be tested in healthy individuals before being implemented in rehabilitation programs.

Objective:

To compare EMG activation of lower-extremity muscles during walking while wearing 2 different ankle-destabilization devices.

Design:

Crossover.

Setting:

Laboratory.

Participants:

15 healthy young adults (5 men, 10 women).

Intervention:

Surface EMG activity was recorded from the anterior tibialis, peroneus longus, lateral gastrocnemius, rectus femoris, biceps femoris, and gluteus medius as subjects walked on a treadmill shod, with an ankle-destabilization boot (ADB), and an ankle-destabilization sandal (ADS).

Main Outcome Measures:

Normalized amplitudes 100 ms before and 200 ms after initial heel contact, time of onset activation relative to initial contact, and percent of activation time across the stride cycle were calculated for each muscle in each condition.

Results:

The precontact amplitudes of the peroneus longus and lateral gastrocnemius and the postcontact amplitudes of the lateral gastrocnemius were significantly greater in the ADB and ADS conditions. In the ADB condition, the rectus femoris and biceps femoris postcontact amplitudes were significantly greater than shod. The peroneus longus and lateral gastrocnemius were activated significantly earlier, and the anterior tibialis, lateral gastrocnemius, and rectus femoris were activated significantly longer across the stride cycle in the ADB and the ADS conditions. In addition, the peroneus longus was activated significantly longer in the ADB condition when compared with shod.

Conclusions:

Both ankle-destabilization devices caused an alteration in muscle activity during walking, which may be favorable to an injured patient. Therefore, implementing these devices in rehabilitation programs may be beneficial to improving neuromuscular control.

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Joseph M. Hart, Jamie L. Leonard and Christopher D. Ingersoll

Context:

Despite recent findings regarding lower extremity function after cryotherapy, little is known of the neuromuscular, kinetic, and kinematic changes that might occur during functional tasks.

Objective:

To evaluate changes in ground-reaction forces, muscle activity, and knee-joint flexion during single-leg landings after 20-minute knee-joint cryotherapy.

Design:

1 × 4 repeated-measures, time-series design.

Setting:

Research laboratory.

Patients or Other Participants:

20 healthy male and female subjects.

Intervention:

Subjects performed 5 single-leg landings before, immediately after, and 15 and 30 minutes after knee-joint cryo-therapy.

Main Outcome Measures:

Ground-reaction force, knee-joint flexion, and muscle activity of the gastrocnemius, hamstrings, quadriceps, and gluteus medius.

Results:

Cryotherapy did not significantly (P > .05) change maximum knee-joint flexion, vertical ground-reaction force, or average muscle activity during a single-leg landing.

Conclusion:

Knee-joint cryotherapy might not place the lower extremity at risk for injury during landing.

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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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John Goetschius, Mark A. Feger, Jay Hertel and Joseph M. Hart

Context: Measurements of center-of-pressure (COP) excursions during balance are common practice in clinical and research settings to evaluate adaptations in postural control due to pathological or environmental conditions. Traditionally measured using laboratory force plates, pressure-mat devices may be a suitable option for clinicians and scientist to measure COP excursions. Objective: Compare COP measures and changes during balance between MatScan® pressure mat and force plate. Design: Validation study. Setting: Laboratory. Participants: 30 healthy, young adults (19 female, 11 male, 22.7 ± 3.4 y, 70.3 ± SD kg, 1.71 ± 0.09 m). Main Outcomes: COP excursions were simultaneously measured using pressure-mat and force-plate devices. Participants completed 3 eyes-open and 3 eyes-closed single-leg balance trials (10 s). Mean of the 3 trials was used to calculate 4 COP variables: medial-lateral and anterior-posterior excursion, total distance, and area with eyes open and eyes closed. Percent change and effect sizes were calculated between eyes-open to eyes-closed conditions for each variable and for both devices. Results: All COP variables were highly correlated between devices for eyes-open and eyes-closed conditions (all r > .92, P < .001). Bland-Altman plots suggest the pressure-mat COP measurements were smaller than those of the force-plate, and the differences between devices appeared to increase as the measurement magnitude increased. Percent change in COP variables was highly correlated between devices (r > .85, P < .001). Cohen d effect sizes between eyes-open and eyes-closed were all large (d > 2.25) and similar in magnitude between devices. Conclusion: COP measures were correlated between devices, but values tended to be smaller using the pressure mat. The pressure mat and force plate detected comparable magnitude changes in COP measurements between eyes-open and eyes-closed. Pressure mats may provide a viable option for detecting large magnitude changes in postural control during short-duration testing.

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Christine L. Berg, Joseph M. Hart, Riann Palmieri-Smith, Kevin M. Cross and Christopher D. Ingersoll

Context:

If ankle joint cryotherapy impairs the ability of the ankle musculature to counteract potentially injurious forces, the ankle is left vulnerable to injury.

Objective:

To compare peroneal reaction to sudden inversion following ankle joint cryotherapy.

Design:

Repeated measures design with independent variables, treatment (cryotherapy and control), and time (baseline, immediately post treatment, 15 minutes post treatment, and 30 minutes post treatment).

Setting:

University research laboratory.

Patients or Other Participants:

Twenty-seven healthy volunteers.

Intervention(s):

An ice bag was secured to the lateral ankle joint for 20 minutes.

Main Outcome Measures:

The onset and average root mean square amplitude of EMG activity in the peroneal muscles was calculated following the release of a trap door mechanism causing inversion.

Results:

There was no statistically significant change from baseline for peroneal reaction time or average peroneal muscle activity at any post treatment time.

Conclusions:

Cryotherapy does not affect peroneal muscle reaction following sudden inversion perturbation.

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Dawn M. Corbin, Joseph M. Hart, Patrick O. McKeon, Christopher D. Ingersoll and Jay Hertel

Context:

Increased plantar cutaneous afferent information may improve postural control.

Objective:

To compare postural control measures between balance conditions with and without textured insoles.

Design:

crossover trial.

Setting:

Research Laboratory.

Patients or Other Participants:

33 healthy subjects (27.4 ± 9.1yrs, 172.6 ± 10.3 cm, 75.4 ± 16.4 kg).

Intervention(s):

Subjects performed 24, 10-second bipedal and unilateral stance balance trials with eyes opened and eyes closed, with and without a textured insole in subjects’ shoes.

Main Outcome Measures:

Average velocity and area of center of pressure (COP) excursions.

Results:

We observed an interaction among balance conditions during bilateral stance, but not during unilateral stance. On average, subjects exhibited greater area and velocity of COP excursions with eyes closed compared to eyes opened. Significant differences in area and velocity of COP excursions were observed during bilateral stance only when subjects were not wearing textured insoles. There were no significant differences while subjects balanced in bilateral stance with textured insoles.

Conclusions:

Increased afferent information from textured insoles improves postural control in bilateral stance.

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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.

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Alyssa Muething, Shellie Acocello, Kimberly A. Pritchard, Stephen F. Brockmeier, Susan A. Saliba and Joseph M. Hart

Context:

Understanding how muscles activate in a population with a previous glenohumeral-joint (GH) injury may help clinicians understand how to build a conservative treatment plan to strengthen or activate the specific muscles in an attempt to reduce recurrent shoulder injury and development of GH laxity.

Objective:

To investigate muscle-activation differences between the previously injured limb of individuals with a history of GH-joint injury and healthy matched controls during functional isometric contractions.

Design:

Case control.

Setting:

University research laboratory.

Participants:

17 individuals (8 women, 9 men; age 22.3 ± 2.6 y, height 172.4 ± 8.8 cm, mass 75.4 ± 16.5 kg) with previous unilateral shoulder pain and 17 (8 women, 9 men; age 22.9 ± 3.9 y, height 170.9 ± 11.3 cm, mass 73.6 ± 22.9 kg) with no history of shoulder pain or injury.

Intervention(s):

Diagnostic ultrasound measurements of the supraspinatus were completed in both resting and contracted states to assess changes in muscle thickness. Manual muscle tests (anterior deltoid, upper trapezius, infraspinatus, lower trapezius, serratus anterior) and functional isometric contractions (forward flexion, scaption, abduction) were measured using electromyography.

Main Outcome Measures:

Peak, normalized activation of each muscle and supraspinatus thickness activation ratio were compared between groups and bilaterally within groups using separate ANOVAs.

Results:

The anterior deltoid was significantly less activated during all functional isometric tasks in previously injured subjects than in healthy subjects (P = .024). In previously injured subjects, the involved limb-lower trapezius was significantly less activated during scaption and abduction tasks than the contralateral side (P = .022 and P = .031, respectively).

Conclusions:

There were decreases in muscle activation in the anterior deltoid between previously injured and healthy people, as well as in the lower trapezius, in previously injured subjects. Understanding the source of muscle-activation deficits can help clinicians focus rehabilitation exercises on specific muscles.