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J. Ty Hopkins

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J. Ty Hopkins and Jason Adolph

Context:

The Omnikinetic closed-chain dynamometer calculates bilateral ankle, knee, and hip moments during a semirecumbent stepping motion against a predetermined load.

Objective:

To establish intersession reliability of several kinetic variables during different load and speed conditions over a 4-wk period.

Subjects:

19 healthy, physically active adults (age 21 ± 2 y, height 174.7 ± 10.5 cm, mass 74.0 ± 17.2 kg).

Measurement:

Peak measurements were recorded from the dominant leg for joint torque, power, root-mean-square (RMS) power, and knee shear.

Results:

Intersession reliability ranges across conditions were ankle torque .422−.947, ankle power .336−.877, ankle RMS .671−.893, knee torque .816−.918, knee power .823−.927, knee RMS .855−.943, knee shear .832−.936, hip torque .436−.752, hip power .691−.918, and hip RMS .448−.895.

Conclusions:

Moderate to strong reliability was observed in most measurements of the ankle and knee, whereas the hip showed increased variability.

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Blaine C. Long and J. Ty Hopkins

Context:

It is reported that thermotherapy decreases motoneuron-pool recruitment. Any decrease in recruitment might have a significant impact on an athlete’s ability to return to competition.

Objective:

To determine whether moist heat application influences involuntary motoneuron-pool recruitment or voluntary plantar-flexion peak torque of the soleus muscle immediately or 30 min after application.

Design:

A 3 × 3 crossover design.

Setting:

Biomechanics laboratory.

Participants:

Eighteen healthy subjects with no history of lower extremity surgery or injury 12 months before the study volunteered.

Intervention:

A series of short-duration, high-intensity stimuli was delivered to the tibial nerve to find the Hmax and Mmax measures. Immediately after the Hmax and Mmax measures, subjects were positioned on an isokinetic dynamometer where they performed 5 submaximal warm-up repetitions. Immediately after the warm-up, 5 maximum-intensity peak plantar-flexion torque repetitions were performed. After the dynamometer measures, subjects returned to the table, where a moist heat pack, no heat pack, or a dry nonheated heat pack was applied.

Main Outcome Measures:

Hmax, Mmax, peak plantar-flexion torque, surface temperature (°C), and ambient temperature (°C).

Results:

Moist heat did not influence the H:Mmax ratio or peak plantar-flexion torque. Temperature increased with moist heat pack. Ambient temperature remained constant.

Conclusions:

Moist heat did not influence involuntary motoneuron-pool recruitment or voluntary peak plantar-flexion torque of the soleus muscle immediately or 30 min after application.

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J. Ty Hopkins and Christopher D. Ingersoll

Objectives:

To define the concept of arthrogenic muscle inhibition (AMI), to discuss its implications in the rehabilitation of joint injury, to discuss the neurophysiologic events that lead to AMI, to evaluate the methods available to measure AM1 and the models that might be implemented to examine AMI, and to review therapeutic interventions that might reduce AMI.

Data Sources:

The databases MEDLINE, SPORTDiscus, and CIHNAL were searched with the terms reflex inhibition, joint mechanoreceptor, Ib interneuron, Hoffmann reflex, effusion, and joint injury. The remaining citations were collected from references of similar papers.

Conclusions:

AMI is a limiting factor in the rehabilitation of joint injury. It results in atrophy and deficiencies in strength and increases the susceptibility to further injury. A therapeutic intervention that results in decreased inhibition, allowing for active exercise, would lead to faster and more complete recovery.

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Mitchell L. Cordova, Lisa S. Jutte, and J. Ty Hopkins

Many types of rehabilitation exercises are used to reestablish lower extremity neuromuscular function and strength following ankle injuries. It has not been established which exercise induces the greatest leg muscle activity, which might allow patients to recover more quickly from their injuries. The purpose of this investigation was to establish which exercises induce the most muscle activity in the medial gastrocnemius (MG), peroneus longus (PL), and tibialis anterior (TA), as measured by integrated electromyography (I-EMG). Participants (N = 24, age = 22 ± .59, mass = 63.5 ± 2.1 kg, ht = 165.7 ± 1.2 cm) conducted five repetitions of each of four exercise conditions for 30 s: one-legged stance (OLS), OLS on trampoline (OLST), T-Band kicks (TBK), and OLS perturbations (OLSP). It was found that the TBK exercise induces greater I-EMG in all three muscles, the OLST exercise stimulates more I-EMG activity in the MG and TA, and the OLSP exercise induces greater I-EMG activity in the TA.

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B. Andrew Krause., J. Ty Hopkins, Christopher D. Ingersoll, Mitchell L. Cordova, and Jeffrey E. Edwards

Objective:

Correlate skin temperature and motoneuron-pool recruitment during cooling and rewarming.

Design:

Within-subjects, correlational analysis. H reflex was correlated to ankle-skin temperature over time using a Pearson product-moment correlation coefficient and a coefficient of determination (R2).

Subjects:

Ten healthy, physically active college students.

Measurements:

Soleus H reflex and ankle-skin interface temperature were measured during ice application and rewarming. Electrical stimulation was delivered to produce 75% of each subject's maximum H reflex.

Results:

Ankle cooling (r = −.95, P < .05) exhibited a strong inverse relationship with soleus H reflex. A positive correlation was observed between rewarming (r = .74, P < .05) and soleus H reflex.

Conclusions:

Temperature accounts for nearly 90% (R2 = .90) of the variability in the soleus H reflex during cooling and 55% (R2 = .55) during rewarming, suggesting that more motoneurons are recruited as temperature decreases. These interactions appear to involve both local and central nervous system functions.

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Jihong Park, W. Matt Denning, Jordan D. Pitt, Devin Francom, J. Ty Hopkins, and Matthew K. Seeley

Context:

Although knee pain is common, some facets of this pain are unclear. The independent effects (ie, independent from other knee injury or pathology) of knee pain on neural activation of lower-extremity muscles during landing and jumping have not been observed.

Objective:

To investigate the independent effects of knee pain on lower-extremity muscle (gastrocnemius, vastus medialis, medial hamstrings, gluteus medius, and gluteus maximus) activation amplitude during landing and jumping, performed at 2 different intensities.

Design:

Laboratory-based, pretest, posttest, repeated-measures design, where all subjects performed both data-collection sessions.

Methods:

Thirteen able-bodied subjects performed 2 different land and jump tasks (forward and lateral) under 2 different conditions (control and pain), at 2 different intensities (high and low). For the pain condition, experimental knee pain was induced via a hypertonic saline injection into the right infrapatellar fat pad. Functional linear models were used to evaluate the influence of experimental knee pain on muscle-activation amplitude throughout the 2 land and jump tasks.

Results:

Experimental knee pain independently altered activation for all of the observed muscles during various parts of the 2 different land and jump tasks. These activation alterations were not consistently influenced by task intensity.

Conclusion:

Experimental knee pain alters activation amplitude of various lower-extremity muscles during landing and jumping. The nature of the alteration varies between muscles, intensities, and phases of the movement (ie, landing and jumping). Generally, experimental knee pain inhibits the gastrocnemius, medial hamstring, and gluteus medius during landing while independently increasing activation of the same muscles during jumping.

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Kazuto Sakita, Matthew K. Seeley, Joseph William Myrer, and J. Ty Hopkins

Context:

Standing and side-lying external-rotation exercises produce high activation of the deltoid and infraspinatus. Slight shoulder abduction during these exercises may decrease deltoid activity and increase infraspinatus activity.

Objective:

To determine if the addition of a towel under the arm during standing and side-lying external rotation affects infraspinatus, middle and posterior deltoid, and pectoralis major activation characteristics compared with a no-towel condition.

Design:

Controlled laboratory study.

Participants:

20 male volunteers (age 26 ± 3 y, height 1.80 ± 0.07 m, mass 77 ± 10 kg) who were right-hand dominant and had bilaterally healthy shoulders with no current cervical pathology and no skin infection or shoulder lesion.

Interventions:

External-rotation exercises without a towel roll (0° shoulder abduction) and with a towel roll (30° shoulder abduction) were performed in a standing and side-lying.

Main Outcome Measures:

Maximal voluntary isometric contraction for the infraspinatus, middle and posterior deltoid, and pectoralis major and external rotation in standing and side-lying with and without a towel roll were performed. Normalized average and peak surface EMG amplitude were compared between the towel conditions during standing and side-lying external rotation.

Results:

Both infraspinatus and pectoralis major activity had no significant differences between the towel conditions in standing and side-lying (P > .05). In standing and side-lying, posterior-deltoid activity was significantly greater with a towel roll (P < .05). Middle-deltoid activity had no significant differences between the towel conditions in standing (P > .05). However, in side-lying, middle-deltoid activity was significantly lower with a towel roll (P < .05).

Conclusion:

Middle-deltoid activity decreased with a towel roll during side-lying exercises. More data are needed to determine if a towel roll could be used to potentially reduce superior glide during external-rotation exercises.

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Matthew K. Seeley, Seong Jun Son, Hyunsoo Kim, and J. Ty Hopkins

Context: Patellofemoral pain (PFP) is often categorized by researchers and clinicians using subjective self-reported PFP characteristics; however, this practice might mask important differences in movement biomechanics between PFP patients. Objective: To determine whether biomechanical differences exist during a high-demand multiplanar movement task for PFP patients with similar self-reported PFP characteristics but different quadriceps activation levels. Design: Cross-sectional design. Setting: Biomechanics laboratory. Participants: A total of 15 quadriceps deficient and 15 quadriceps functional (QF) PFP patients with similar self-reported PFP characteristics. Intervention: In total, 5 trials of a high-demand multiplanar land, cut, and jump movement task were performed. Main Outcome Measures: Biomechanics were compared at each percentile of the ground contact phase of the movement task (α = .05) between the quadriceps deficient and QF groups. Biomechanical variables included (1) whole-body center of mass, trunk, hip, knee, and ankle kinematics; (2) hip, knee, and ankle kinetics; and (3) ground reaction forces. Results: The QF patients exhibited increased ground reaction force, joint torque, and movement, relative to the quadriceps deficient patients. The QF patients exhibited: (1) up to 90, 60, and 35 N more vertical, posterior, and medial ground reaction force at various times of the ground contact phase; (2) up to 4° more knee flexion during ground contact and up to 4° more plantarflexion and hip extension during the latter parts of ground contact; and (3) up to 26, 21, and 48 N·m more plantarflexion, knee extension, and hip extension torque, respectively, at various times of ground contact. Conclusions: PFP patients with similar self-reported PFP characteristics exhibit different movement biomechanics, and these differences depend upon quadriceps activation levels. These differences are important because movement biomechanics affect injury risk and athletic performance. In addition, these biomechanical differences indicate that different therapeutic interventions may be needed for PFP patients with similar self-reported PFP characteristics.

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Blaine C. Long, Kenneth L. Knight, Ty Hopkins, Allen C. Parcell, and J. Brent Feland

Context:

It is suggested that postinjury pain is difficult to examine; thus, investigators have developed experimental pain models. To minimize pain, cryotherapy (cryo) is applied, but reports on its effectiveness are limited.

Objective:

To investigate a pain model for the anterior knee and examine cryo in reducing the pain.

Design:

Controlled laboratory study.

Setting:

Therapeutic modality laboratory.

Participants:

30 physically active healthy male subjects who were free from any lower extremity orthopedic, neurological, cardiovascular, or endocrine pathologies.

Main Outcome Measures:

Perceived pain was measured every minute. Surface temperature was also assessed in the center of the patella and the popliteal fossa.

Results:

There was a significant interaction between group and time (F68,864 = 3.0, P = .0001). At the first minute, there was no difference in pain between the 3 groups (saline/cryo = 4.80 ± 4.87 mm, saline/sham = 2.80 ± 3.55 mm, no saline/cryo = 4.00 ± 3.33 mm). During the first 5 min, pain increased from 4.80 ± 4.87 to 45.90 ± 21.17 mm in the saline/cryo group and from 2.80 ± 3.55 to 31.10 ± 20.25 mm in the saline/sham group. Pain did not change within the no-saline/cryo group, 4.00 ± 3.33 to 1.70 ± 1.70 mm. Pain for the saline/sham group remained constant for 17 min. Cryo decreased pain for 16 min in the saline/cryo group. There was no difference in preapplication surface temperature between or within each group. No change in temperature occurred within the saline/sham. Cooling and rewarming were similar in both cryo groups. Ambient temperature fluctuated less than 1°C during data collection.

Conclusion:

Intermittent infusion of sterile 5% hypertonic saline may be a useful experimental pain model in establishing a constant level of pain in a controlled laboratory setting. Cryotherapy decreased the induced anterior knee pain for 16 min.