J. Ty Hopkins

Peroneal Activation Deficits in Persons With Functional Ankle Instability

Background Functional ankle instability (FAI) may be prevalent in as many as 40% of patients after acute lateral ankle sprain. Altered afference resulting from damaged mechanoreceptors after an ankle sprain may lead to reflex inhibition of surrounding joint musculature. This activation deficit, referred to as arthrogenic muscle inhibition (AMI), may be the underlying cause of FAI. Incomplete activation could prevent adequate control of the ankle joint, leading to repeated episodes of instability. Hypothesis Arthrogenic muscle inhibition is present in the peroneal musculature of functionally unstable ankles and is related to dynamic peroneal muscle activity. Study Design Cross-sectional study; Level of evidence, 3. Methods Twenty-one (18 female, 3 male) patients with unilateral FAI and 21 (18 female, 3 male) uninjured, matched controls participated in this study. Peroneal maximum H-reflexes and M-waves were recorded bilaterally to establish the presence or absence of AMI, while electromyography (EMG) recorded as patients underwent a sudden ankle inversion perturbation during walking was used to quantify dynamic activation. The H:M ratio and average EMG amplitudes were calculated and used in data analyses. Two-way analyses of variance were used to compare limbs and groups. A regression analysis was conducted to examine the association between the H:M ratio and the EMG amplitudes. Results The FAI patients had larger peroneal H:M ratios in their nonpathological ankle (0.399 ± 0.185) than in their pathological ankle (0.323 ± 0.161) (P = .036), while no differences were noted between the ankles of the controls (0.442 ± 0.176 and 0.425 ± 0.180). The FAI patients also exhibited lower EMG after inversion perturbation in their pathological ankle (1.7 ± 1.3) than in their uninjured ankle (EMG, 3.3 ± 3.1) (P < .001), while no differences between legs were noted for controls (P > .05). No significant relationship was found between the peroneal H:M ratio and peroneal EMG (P > .05). Conclusion Arthrogenic muscle inhibition is present in the peroneal musculature of persons with FAI but is not related to dynamic muscle activation as measured by peroneal EMG amplitude. Reversing AMI may not assist in protecting the ankle from further episodes of instability; however dynamic muscle activation (as measured by peroneal EMG amplitude) should be restored to maximize ankle stabilization. Dynamic peroneal activity is impaired in functionally unstable ankles, which may contribute to recurrent joint instability and may leave the ankle vulnerable to injurious loads.

National Athletic Trainers' Association Position Statement: Conservative Management and Prevention of Ankle Sprains in Athletes

OBJECTIVE To present recommendations for athletic trainers and other allied health care professionals in the conservative management and prevention of ankle sprains in athletes. BACKGROUND Because ankle sprains are a common and often disabling injury in athletes, athletic trainers and other sports health care professionals must be able to implement the most current and evidence-supported treatment strategies to ensure safe and rapid return to play. Equally important is initiating preventive measures to mitigate both first-time sprains and the chance of reinjury. Therefore, considerations for appropriate preventive measures (including taping and bracing), initial assessment, both short- and long-term management strategies, return-to-play guidelines, and recommendations for syndesmotic ankle sprains and chronic ankle instability are presented. RECOMMENDATIONS The recommendations included in this position statement are intended to provide athletic trainers and other sports health care professionals with guidelines and criteria to deliver the best health care possible for the prevention and management of ankle sprains. An endorsement as to best practice is made whenever evidence supporting the recommendation is available.

Deficits in peroneal latency and electromechanical delay in patients with functional ankle instability

The purpose of this study was to compare alterations in peroneal latency and electromechanical delay (EMD) following an inversion perturbation during walking in patients with functional ankle instability (FAI) and with a matched control group. Peroneal latency and EMD were measured from 21 patients with unilateral FAI and 21 controls. Latencies were collected during a random inversion perturbation while walking. EMD measures were collected during stance using a percutaneous stimulus. Two‐way ANOVAs were used to detect differences between leg (affected, unaffected) and group (FAI, Control). Functionally unstable ankles displayed delayed peroneus longus (PL) latencies and EMD when compared to the unaffected leg and a matched control group. Peroneal latency and EMD deficits could contribute to recurrence of ankle injury in FAI subjects. How these deficits are associated with the chronic symptoms associated with FAI remains unclear, but gamma activation and subsequent muscle spindle sensitivity likely play a role.

A COMPARISON OF VOLUNTARY AND INVOLUNTARY MEASURES OF ELECTROMECHANICAL DELAY

Electromechanical delay (EMD) is a measurement used to assess the mechanical lag between muscle activation onset and force production. EMD measurements may be performed by voluntary or electrically evoked muscle activation. This study compared gastrocnemius EMD during voluntary and involuntary contractions and assessd the intrasession reliability of each set of measurements. Subjects were 15 volunteers (age 21 ± 2 years, ht 171.8 ± 10.0 cm, mass 76.1 ± 13.4 kg). EMD measurements were recorded from the medial head of the gastrocnemius of each subject during voluntary and involuntary contractions. Order was counterbalanced between subjects. Subjects stood with the dominant leg on a force plate, the nondominant next to the force plate, and with their hands in contact with a bar in front of them. A supramaximal percutaneous stimulus was applied to the tibial nerve in the popliteal fossa for involuntary (electrically evoked) contractions. For voluntary contractions, subjects were instructed to rise up on the toes as quickly as possible. Four trials were collected for each condition with 30 s of rest between each. Repeated measures ANOVAs were performed for each condition to calculate an ICC (2,1). Means of the 4 trials for each condition were used to detect differences between groups. EMD was greater in the voluntary condition (22.8 ± 8.2 ms) compared to the involuntary condition (9.7 ± 3.1 ms; p < .001). Intrasession reliability for each condition was very strong (involuntary ICC (2,1) = .977; voluntary ICC (2,1) = .972). EMD measured during a single leg stance is much shorter when measured during an electrically evoked (voluntary) contraction. The difference in EMD between conditions is likely the result of differences in recruitment during the two types of contractions. Reliability within a measurement session was very strong for each of the conditions.

Alterations in evertor/invertor muscle activation and center of pressure trajectory in participants with functional ankle instability

Participants with ankle instability demonstrate more foot inversion during the stance phase of gait than able-bodied subjects. Invertor excitation, coupled with evertor inhibition may contribute to this potentially injurious position. The purpose of this experiment was to examine evertor/invertor muscle activation and foot COP trajectory during walking in participants with functional ankle instability (FI). Twelve subjects were identified with FI and matched to healthy controls. Tibialis anterior (TA) and peroneus longus (PL) electromyography (EMG), as well as COP, were recorded during walking. Functional analyses were used to detect differences between FI and control subjects with respect to normalized EMG and COP trajectory during walking. Relative to matched controls, COP trajectory was more laterally deviated in the FI group from 20% to 90% of the stance phase. TA activation was greater in the FI group from 15% to 30% and 45% to 70% of stance. PL activation was greater in the FI group at initial heel contact and toe off and trended lower from 20% to 40% of stance in the FI group. Altered motor strategies appear to contribute to COP deviations in FI participants and may increase the susceptibility to repeated ankle inversion injury.

Effects of Ankle Joint Effusion on Lower Leg Function

BackgroundInversion ankle sprains are among the most frequently encountered injuries in and outside of sport. Altered feedback from joint damage and/or edema may negatively affect dynamic stabilization, thereby increasing the patients’ susceptibility to further injury. In order to understand better how the sensorimotor system responds to the presence of ankle edema during a functional task, further examination is warranted. ObjectiveTo quantify muscle activation in the peroneal, tibialis anterior, and soleus musculature as well as to determine ankle joint peak torque, peak power, and root mean square (RMS) power during a closed kinetic chain activity following artificial ankle effusion. DesignDependent variables were compared within subjects across time intervals and between groups. SettingAll data were collected in the biomechanics laboratory. ParticipantsSubjects were 20 healthy, neurologically sound volunteers (age 21.9 ± 2.1 y, height 174.5 ± 9.3 cm, mass 79.3 ± 15.9 kg) with no lower extremity injuries. InterventionsSubjects were prepared for surface electrodes on the peroneus longus (PL), tibialis anterior (TA), soleus (Sol), and medial malleolus (ground). Anthropometric measures for the lower extremity were recorded for use by the Omnikinetic closed chain dynamometer. Measurements were taken prior to ankle effusion (baseline), immediately following effusion (post), and again at 30 minutes. Main Outcome MeasurementsTesting consisted of 6 repetitions at 35% of 1-repetition max and a constant speed of 1.5 Hz. Separate two-way MANOVAs with repeated measures on time intervals were used to detect differences between groups (effusion and control) over time for torque, power, and RMS power and for peak and average EMG. ResultsAn overall time × group interaction was detected for EMG (F4,72 = 3.878; P = 0.007) and kinetic variables (F6,70 = 5.55; P = 0.0001). Average and peak PL EMG decreased immediately following effusion (Sidak’s; P = 0.048), and average EMG remained depressed 30 minutes following effusion (Sidak’s; P = 0.02). Immediately posteffusion, a decrease in ankle torque was detected (Sidak’s; P = 0.007). No differences in TA or Sol EMG, power, or RMS power were detected (P > 0.05). ConclusionsDecreases in ankle plantarflexion torque and PL EMG indicate that a neuromuscular deficit exists in the presence of edema that could increase the susceptibility for further ankle injury.

Whole-body vibration strengthening compared to traditional strengthening during physical therapy in individuals with total knee arthroplasty

ABSTRACT This study investigated the use of whole-body vibration (WBV) as an alternative strengthening regimen in the rehabilitation of individuals with total knee arthroplasty (TKA) compared with traditional progressive resistance exercise (TPRE). Individuals post TKA (WBV n = 8; TPRE n = 8) received physical therapy with WBV or with TPRE for 4 weeks. Primary dependent variables were knee extensor strength, quadriceps muscle activation, mobility, pain, and range of motion (ROM). There was a significant increase in knee extensor strength and improvements in mobility, as measured by maximal volitional isometric contraction and the Timed Up and Go Test (TUG), respectively, for both groups (p < 0.01). The WBV knee extensor strength improved 84.3% while TPRE increased 77.3%. TUG scores improved 31% in the WBV group and 32% for the TPRE group. There were no significant differences between groups for strength or muscle activation (Hotellings T2 = 0.42, p = 0.80) or for mobility (F = 0.54; p = 0.66). No adverse side effects were reported in either group. In individuals with TKA, both WBV and TPRE showed improved strength and function. Influence of WBV on muscle activation remains unclear, as muscle activation levels were near normal for both groups.

Reflex inhibition of electrically induced muscle cramps in hypohydrated humans.

INTRODUCTION Anecdotal evidence suggests that ingesting small volumes of pickle juice relieves muscle cramps within 35 s of ingestion. No experimental evidence exists supporting the ingestion of pickle juice as a treatment for skeletal muscle cramps. METHODS On two different days (1 wk apart), muscle cramps were induced in the flexor hallucis brevis (FHB) of hypohydrated male subjects (approximately 3% body weight loss and plasma osmolality approximately 295 mOsm x kg(-1) H2O) via percutaneous tibial nerve stimulation. Thirty minutes later, a second FHB muscle cramp was induced and was followed immediately by the ingestion of 1 mL x kg(-1) body weight of deionized water or pickle juice (73.9 +/- 2.8 mL). RESULTS Cramp duration and FHB EMG activity during the cramp were quantified, as well as the change in plasma constituents. Cramp duration (water = 151.9 +/- 12.9 s and pickle juice = 153.2 +/- 23.7 s) and FHB EMG activity (water = 60% +/- 6% and pickle juice = 68% +/- 9% of maximum voluntary isometric contraction EMG activity) were similar during the initial cramp induction without fluid ingestion (P > 0.05). During FHB muscle cramp induction combined with fluid ingestion, FHB EMG activity was again similar (water = 55% +/- 9% and pickle juice = 66% +/- 9% of maximum voluntary isometric contraction EMG activity, P > 0.05). However, cramp duration was 49.1 +/- 14.6 s shorter after pickle juice ingestion than water (84.6 +/- 18.5 vs 133.7 +/- 15.9 s, respectively, P < 0.05). The ingestion of water or pickle juice had little impact on plasma composition 5 min after ingestion. CONCLUSIONS Pickle juice, and not deionized water, inhibits electrically induced muscle cramps in hypohydrated humans. This effect could not be explained by rapid restoration of body fluids or electrolytes. We suspect that the rapid inhibition of the electrically induced cramps reflects a neurally mediated reflex that originates in the oropharyngeal region and acts to inhibit the firing of alpha motor neurons of the cramping muscle.

Quadriceps activation normative values and the affect of subcutaneous tissue thickness

Calculation of the central activation ratio (CAR) using the superimposed burst technique (SIB) is widely used. 0.95 is considered a normal value of the CAR in healthy subjects, but it has not been objectively examined. Since an electrical stimulation penetrates the subcutaneous tissue, the intensity of electrical stimulation may vary depending on the subcutaneous tissue thickness. Subjects performed a maximal voluntary isometric contraction (MVIC) of the quadriceps with the knee at 90°. Once the MVIC reached a plateau, an electrical stimulation was manually delivered to the quadriceps. Quadriceps CAR was quantified using the equation: CAR=MVIC/MVIC+SIB torque. Quadriceps subcutaneous thickness was measured using ultrasound imaging and skinfolder pinch calipers. CAR values were estimated at 0.95 ± 0.04 for dominant and 0.93 ± 0.05 for non-dominant limbs. Pearsons correlation coefficient revealed that there were negative correlations for quadriceps torque output (Nm/kg) and subcutaneous tissue thickness measured by ultrasound imaging (dominant: r=-0.54, p<0.001; non-dominant: r=-0.53, p<0.001). We found no relationship between CAR and subcutaneous tissue thickness. A CAR of 0.95 may be considered full activation in healthy young adults, and CAR in healthy adults generated by the SIB technique may not be dependent on subcutaneous thickness.

A Novel Experimental Knee-Pain Model Affects Perceived Pain and Movement Biomechanics

CONTEXT Knee injuries are prevalent, and the associated knee pain is linked to disability. The influence of knee pain on movement biomechanics, independent of other factors related to knee injuries, is difficult to study and unclear. OBJECTIVE (1) To evaluate a novel experimental knee-pain model and (2) better understand the independent effects of knee pain on walking and running biomechanics. DESIGN Crossover study. SETTING Biomechanics laboratory. PATIENTS OR OTHER PARTICIPANTS Twelve able-bodied volunteers (age = 23 ± 3 years, height = 1.73 ± 0.09 m, mass = 75 ± 14 kg). INTERVENTION(S) Participants walked and ran at 3 time intervals (preinfusion, infusion, and postinfusion) for 3 experimental conditions (control, sham, and pain). During the infusion time interval for the pain and sham conditions, hypertonic or isotonic saline, respectively, was continuously infused into the right infrapatellar fat pad for 22 minutes. MAIN OUTCOME MEASURE(S) We used repeated-measures analyses of variance to evaluate the effects of time and condition on (1) perceived knee pain and (2) key biomechanical characteristics (ground reaction forces, and joint kinematics and kinetics) of walking and running (P < .05). RESULTS The hypertonic saline infusion (1) increased perceived knee pain throughout the infusion and (2) reduced discrete characteristics of each component of the walking ground reaction force, walking peak plantar-flexion angle (range = 62°-67°), walking peak plantar-flexion moment (range = 95-104 N·m), walking peak knee-extension moment (range = 36-49 N·m), walking peak hip-abduction moment (range = 62-73 N·m), walking peak support moment (range = 178-207 N·m), running peak plantar-flexion angle (range = 38°-77°), and running peak hip-adduction angle (range = 5-21°). CONCLUSIONS This novel experimental knee pain model consistently increased perceived pain during various human movements and produced altered running and walking biomechanics that may cause abnormal knee joint-loading patterns.