A functional fatiguing protocol and deceleration time of the shoulder from an internal rotation perturbation.

CONTEXT: Muscular fatigue impedes sensorimotor function and may increase the risk of shoulder injury during activity. The effects of fatigue on the sensorimotor system of the shoulder have been studied with various results. Deceleration times have been used to study neuromuscular control of the shoulder; however, no studies involving the effects of fatigue on deceleration times have been reported. OBJECTIVE: To compare shoulder deceleration times after a shoulder internal rotation perturbation before and after a repetitive throwing exercise protocol. DESIGN: A 2 x 2 repeated-measures design. SETTING: Exercise and sport injury laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty healthy, recreationally active men (age = 24.76 +/- 4.03 years, height = 178.41 +/- 8.36 cm, mass = 80.16 +/- 15.20 kg) volunteered to participate in the study. To ensure familiarity with the overhead motion, all subjects chosen had previously participated in an overhead throwing sport. INTERVENTION(S): The independent variables were time (preintervention and postintervention) and session (experimental and control). The intervention consisted of continuous overhead throwing. The subjects were considered fatigued when a 10% decrease in velocity was noted on 3 consecutive pitches. MAIN OUTCOME MEASURE(S): Time necessary to decelerate from an internal rotation perturbation. RESULTS: Deceleration time was significantly increased by the fatiguing intervention ( P = .001). CONCLUSIONS: The decreased ability to decelerate may be an adaptive response by the subjects to dissipate a lower percentage of force per second.

Sex differences in valgus knee angle during a single-leg drop jump.

CONTEXT: Sex differences in lower extremity landing mechanics and muscle activation have been identified as potential causative factors leading to the increased incidence of anterior cruciate ligament injuries in female athletes. Valgus knee alignment places greater strain on the anterior cruciate ligament than a more neutral alignment. Gluteus medius (GM) activation may stabilize the leg and pelvis during landing, limiting valgus knee motion and potentially preventing anterior cruciate ligament injury. OBJECTIVE: To determine if frontal-plane knee angle and GM activation differ between the sexes at initial contact and maximal knee flexion during a single-leg drop landing. DESIGN: Between-groups design. SETTING: Motion analysis laboratory. PATIENTS OR OTHER PARTICIPANTS: Thirty-two healthy subjects between the ages of 18 and 30 years. INTERVENTION(S): The independent variables were sex (male or female) and position (initial contact or maximal knee flexion). MAIN OUTCOME MEASURE(S): Frontal-plane knee angle and GM average root mean square (aRMS) amplitude. RESULTS: At initial contact, women landed in knee valgus and men landed in knee varus (P < .025). At maximal knee flexion, both men and women were in a position of knee varus, but the magnitude of varus was less in women than in men (P < .025). The GM aRMS amplitude was greater at maximal knee flexion than at initial contact (P < .025); however, male GM aRMS did not differ from female GM aRMS amplitude at either position (P > .025). CONCLUSIONS: Women tended to land in more knee valgus before and at impact than men. The GM muscle activation did not differ between the sexes and, thus, does not appear to be responsible for the sex differences in knee valgus. The excessive valgus knee angles displayed in women may help to explain the sex disparity in anterior cruciate ligament injury.

Peripheral ankle cooling and core body temperature.

CONTEXT: Exposure of the human body to cold is perceived as a stressor and results in a sympathetic response geared at maintaining core temperature. Application of ice to the periphery may lead to a decrease in core temperature, which may counteract the therapeutic effects of cryotherapy. OBJECTIVE: To determine if core temperature is lowered by the application of an ice bag to the ankle joint complex. DESIGN: A within-subjects, repeated-measures design. SETTING: The University of Virginia General Clinical Research Center. PATIENTS OR OTHER PARTICIPANTS: Twenty-three healthy adults aged 19 to 39 years. INTERVENTION(S): Subjects were admitted to the hospital on 2 separate occasions. During one admission, subjects had a 20-minute ice treatment applied to their ankles; in the other admission, a bag of marbles was applied. Temperature measurements were recorded at 6 time intervals: baseline (before ice application), immediately after ice application, 10 and 20 minutes after ice application, and 10 and 20 minutes after ice removal. MAIN OUTCOME MEASURE(S): We measured core temperature and ankle and soleus muscle surface temperatures. A mixed-effects model analysis of variance with repeated measures was used to determine if differences existed in core temperature and ankle and soleus surface temperatures between conditions (cryotherapy and control) and over time. RESULTS: Core temperature did not change after ice application or ice removal (P > 0.05). The average core temperatures during the cryotherapy and control conditions were 36.72 degrees C +/- 0.42 degrees C and 36.45 degrees C +/- 1.23 degrees C, respectively. CONCLUSIONS: A 20-minute cryotherapy treatment applied to the ankle did not alter core temperature.

Performance-based physical functioning in African-American and Caucasian women at midlife: considering body composition, quadriceps strength, and knee osteoarthritis.

In 2000, body composition, x-ray-defined knee osteoarthritis, and self-reported knee pain information from a cross-sectional, community-based study of 211 African-American and 669 Caucasian women in southeast Michigan (mean age, 47 years) was related to performance-based physical functioning measures to characterize development of functional limitations. Body composition was assessed with bioelectrical impedance. Functioning measures were gait assessment, timed walk, timed stair climb with and without videography, and isometric quadriceps strength. Knee osteoarthritis was determined by Kellgren-Lawrence score from radiography, whereas knee pain was self-reported. Almost 31% of mid-aged women walked at functionally inadequate speeds, and over 12% walked at speeds considered typical of frailty in older women. Ten percent of women had skeletal muscle mass levels less than a proposed cutpoint for increased physical disability risk in older adults. Gait measures correlates included increasing age, increasing fat mass (in kilograms), knee joint pain, and reduced quadriceps strength. Stair climbing correlates included skeletal muscle mass (in kilograms) and its change, painful knee osteoarthritis, and reduced quadriceps strength. Race differences in walking measures and stair climbing time diminished when the authors accounted for other factors. Compromised physical functioning began earlier than expected, with indications that approximately 12-31% of women might benefit from interventions to forestall future decline.

Intersession reliability of a protocol to assess reflex activation history in the vastus medialis.

The purpose of this study was to determine the reliability of a protocol to assess reflex activation history in the vastus medialis. Eight subjects reported to the laboratory on two occasions. Reflex activation history was assessed by delivering two stimuli of the same intensity 80 ms apart. The dependent variable evaluated was the percentage of the unconditioned reflex amplitude. Eight trials were elicited and averaged on each day. An intraclass correlation coefficient (ICC 2,1) was used to estimate intersession reliability. The ICC for the protocol was found to be 0.9647. The results of this investigation indicate that this technique can reliably estimate reflex activation history in the vastus medialis.

Pre-synaptic modulation of quadriceps arthrogenic muscle inhibition.

Arthrogenic muscle inhibition (AMI) impedes rehabilitation following knee joint injury by preventing activation of the quadriceps. AMI has been attributed to neuronal reflex activity in which altered afferent input originating from the injured joint results in a diminished efferent motor drive to the quadriceps muscles. Beginning to understand the mechanisms responsible for muscle inhibition following joint injury is vital to control or eliminate this phenomenon. Therefore, the purpose of this investigation is to determine if quadriceps AMI is mediated by a presynaptic regulatory mechanism. Eight adults participated in two sessions: in one session their knee was injected with saline and in the other session it was not. The maximum Hoffmann reflex (H-reflex), M-wave, reflex activation history, plasma epinephrine, and norepinephrine were recorded at: baseline, post needle stick, post lidocaine, and 25 and 45 min post effusion. Measures for the control condition were matched to the effusion condition. The percent of the unconditioned reflex amplitude for reflex activation history and the maximum H-reflex were decreased at 25 and 45 min post effusion as compared to measures taken at baseline, post needle stick, and post lidocaine (P<0.05). No differences were noted for the maximum M-wave or plasma epinephrine and norepinephrine levels in either the effusion or noneffusion admission (P>0.05). No differences were detected at any time interval for any measure during the control admission (P>0.05). Quadriceps AMI elicited via an experimental knee joint effusion is, at least in part, mediated by a presynaptic mechanism.

Arthrogenic muscle inhibition in the leg muscles of subjects exhibiting functional ankle instability.

BACKGROUND: Functional ankle instability or a subjective report of ;;giving way'' at the ankle may be present in up to 40% of patients after a lateral ankle sprain. Damage to mechanoreceptors within the lateral ankle ligaments after injury is hypothesized to interrupt neurologic feedback mechanisms resulting in functional ankle instability. The altered input can lead to weakness of muscles surrounding a joint, or arthrogenic muscle inhibition. Arthrogenic muscle inhibition may be the underlying cause of functional ankle instability. Establishing the involvement of arthrogenic muscle inhibition in functional ankle instability is critical to understanding the underlying mechanisms or chronic ankle instability. The purpose of this investigation was to determine if arthrogenic muscle inhibition is present in the ankle joint musculature of patients exhibiting unilateral functional ankle instability. METHODS: Twenty-nine subjects, 15 with unilateral functional ankle instability and 14 healthy control subjects, consented to participate. Bilateral soleus, peroneal, and tibialis anterior H-reflex and M-wave recruitment curves were obtained. Maximal H-reflex and maximal M-wave values were identified and the H:M ratios were calculated for data analysis. Separate 1 x 2 ANOVA were done for both the functional ankle instability and control groups to evaluate differences between limbs on the H:M ratios. Bonferroni multiple comparison procedures were used for post hoc comparisons (p < or = 0.05). RESULTS: The soleus and peroneal H:M ratios for subjects with functional ankle instability were smaller in the injured limb when compared with the uninjured limb (p < 0.05). No limb difference was detected for the tibialis anterior H:M ratio in the functional ankle instability group (p = 0.904). No side-to-side differences were detected for the H:M ratios in patients reporting no history of ankle injury (p > 0.05). CONCLUSIONS: Depressed H:M ratios in the injured limb suggest that arthrogenic muscle inhibition is present in the ankle musculature of patients exhibiting functional ankle instability. Establishing and using therapeutic techniques to reverse arthrogenic muscle inhibition may reduce the incidence of functional ankle instability.

Arthrogenic muscle response induced by an experimental knee joint effusion is mediated by pre- and post-synaptic spinal mechanisms.

Knee joint effusion results in quadriceps inhibition and is accompanied by increased excitability in the soleus musculature. The purpose of this study was to determine if soleus arthrogenic muscle response is regulated by pre- or post-synaptic spinal mechanisms. Ten healthy adults (two females and eight males) were measured on two occasions. At the first session, subjects had their knee injected with 60 ml of saline and in the other session they did not. Pre- and post-synaptic spinal mechanisms were measured at baseline, immediately following a needle stick, immediately following a Xylocaine injection, and 25 and 45 min post-saline injection. A mixed effects model for repeated measures was used to analyze each dependent variable. The a priori alpha level was set a P < or = 0.05. The percentage of the unconditioned reflex amplitude for recurrent inhibition (P < 0.0001) and reflex activation history (P < 0.0001) significantly increased from baseline at 25 and 45 min post-effusion. Soleus arthrogenic muscle response seen following knee joint effusion is mediated by both pre- and post-synaptic mechanisms. In conclusion, the arthrogenic muscle response seen in the soleus musculature following joint effusion is regulated by both pre- and post-synaptic control mechanisms. Our data are the first step in understanding the neural networks involved in the patterned muscle response that occurs following joint effusion.

An experimental knee joint effusion does not affect plasma catecholamine concentration in humans.

Knee joint effusion causes quadriceps inhibition and is accompanied by increased soleus muscle excitability. In order to reverse the neurological alterations that occur to the musculature following effusion, we need to understand the extent of neural involvement. Ten healthy adults were tested on two occasions; during one session, subjects had their knees injected with saline and in the other admission, they did not. Soleus Hmax, Mmax, plasma epinephrine, and norepinephrine concentrations were obtained at five intervals. Results showed that Hmax increased following the effusion, while norepinephrine and epinephrine levels were not altered. We suggest that the soleus facilitation seen following knee effusion results from stimulation of joint mechanoreceptors and removal of descending spinal and supraspinal inhibition and is not the result of a sympathetic response.

The hoffmann reflex: methodologic considerations and applications for use in sports medicine and athletic training research.

OBJECTIVE: To discuss the proper methods used to elicit the Hoffmann reflex (H-reflex) and to present different situations in which this tool can be used in sports medicine research. DATA SOURCES: We searched MEDLINE and SPORT Discus from 1960 to 2004 using the key words Hoffmann reflex, H-reflex, and methodology. The remaining citations were collected from references of similar papers. DATA SYNTHESIS: Numerous authors have used the H-reflex as a tool to examine neurologic conditions. However, few have used the H-reflex to examine neuromuscular impairments after sport injuries. Several studies were available describing the appropriate methods to elicit the H-reflex and examining the reliability of this measurement in different muscles. CONCLUSIONS/RECOMMENDATIONS: The H-reflex is a valuable tool to evaluate neurologic function in various populations. However, because of the sensitivity of this measurement to extraneous factors, care must be taken when eliciting the H-reflex. We discuss recommendations on how to elicit the H-reflex and how to appropriately present methods in a manuscript.

Arthrogenic muscle inhibition is not present in the limb contralateral to a simulated knee joint effusion.

OBJECTIVE: The purpose of this investigation was to estimate bilateral neuromuscular activity in the vastus medialis on induction of a unilateral knee joint effusion. DESIGN: Eight subjects each were assigned to effusion or control groups. The effusion group had 60 ml of sterile saline injected into their superolateral knee joint capsules. The control group rested for 8 mins. Bilateral recruitment curves for the Hoffmann reflex (H-reflex) and muscle response (M-wave) were obtained before and 10, 20, and 30 mins after the effusion or rest. The maximum H-reflex (Hmax), maximum M-wave (Mmax), and the Hmax/Mmax ratio were utilized for data analysis. RESULTS: Both Hmax and Hmax/Mmax ratios decreased from the baseline measure in the effused vastus medialis, whereas no changes were detected on the contralateral side. Effused subjects demonstrated decreased motoneuron pool excitability in the effused limb, whereas control subjects did not differ from baseline. CONCLUSIONS: Knee joint effusion results in ipsilateral but not contralateral impairment of quadriceps function. Rehabilitation protocols after knee joint injury should focus on ipsilateral neuromuscular and mechanical alterations that occur as the result of joint damage.

A single dose of Ginkgo biloba does not affect soleus motoneuron pool excitability.

EGb 761 has been shown to increase acetylcholine synthesis and release and increase cholinergic receptors leading to an increase in cholinergic neurotransmission. These effects may be observed in the neuromuscular system, manifested by changes in motoneuron pool excitability as measured by the Hoffmann reflex to motor response (H/M) ratio. The objective was to determine whether a single dose of EGb 761 affects motoneuron pool excitability of the soleus muscle as measured by the H/M ratio. Following initial soleus H/M measurements, 20 healthy volunteers were randomly assigned to 1 of 3 treatment groups (control, 180 g cellulose placebo, and 180 g EGb 761). H/M ratios were recorded 1, 2, and 3 hours post treatment. A 3 x 4 repeated-measures analysis of variance was used to analyze differences in H/M ratio between treatments. No differences were observed between treatments (p = 0.75) or over time (p = 0.17), and there was not a treatment by time interaction (p = 0.27). A single dose of 180 g of EGb 761 does not affect soleus motoneuron pool excitability.

The effect of a simulated knee joint effusion on postural control in healthy subjects.

OBJECTIVE: To determine the effects of a simulated knee joint effusion on center of pressure (COP) path and mean power frequency (MPF) during standing. DESIGN: Quasi-experimental design. SETTING: Sports injury research laboratory in a university setting. PARTICIPANTS: Twenty healthy volunteers, 10 of whom (age, 20.1+/-2.4y; height, 168.0+/-8.1cm; weight, 70.4+/-13.3kg) were assigned to an effusion group and 10 of whom (age, 25+/-3.8y; height, 169.4+/-8.9cm; weight, 74.7+/-7.7kg) were assigned to a control group. INTERVENTIONS: COP data were collected before and after a 60-mL injection of sterile saline into the knee joint space. MAIN OUTCOME MEASURES: COP path and mediolateral and anteroposterior MPF. RESULTS: COP path decreased after the effusion (pre-effusion mean, 92.2+/-21.9cm; posteffusion mean, 77.27+/-23.0cm). No change was found within the control group for COP path (P>.05). No differences were detected before or after joint effusion when the MPF was examined (P>.05). CONCLUSIONS: Possible explanations for the improved postural control after the effusion include additional somatosensory feedback, an augmented neural drive to the soleus, and/or increased capsular tension.

Simultaneous Hoffmann reflex measurements in multiple muscles around the ankle.

Measurement of the Hoffmann reflex (H-reflex) provides an estimate of alpha motoneuron activity in the target motoneuron (MN) pool. The H-reflex has been assessed for a wide variety of reasons in neuroscience research. However, the majority of protocols have focused on the assessment of only one muscle and its corresponding motoneuron pool at any instant. Previously established protocols do not simultaneously assess reflex activity in multiple muscles elicited from a single stimulation. This new protocol allows for assessment of alpha motoneuron activity in three muscles around the ankle joint from a single stimulus to the sciatic nerve. To elicit the responses, the sciatic nerve was stimulated just prior to its bifurcation into the tibial and common peroneal nerves in the popliteal fossa. Electromyographic recording electrodes were placed on the tibialis anterior, peroneal longus, and soleus muscles. The 1-ms square wave pulse was delivered every 15 s during the recruitment curve mapping. The maximum H reflex and M waves were measured in each muscle and their ratios calculated. The measurement of these ratios simultaneously allows for assessment of the cumulative alpha motoneuron activity about the ankle at a given point in time.

Intersession reliability for H-reflex measurements arising from the soleus, peroneal, and tibialis anterior musculature.

The Hoffman reflex (H-reflex) has been widely used throughout neuroscience research, as it allows for the assessment of alpha motoneuron excitability arising from a specific motoneuron pool. Recently, a protocol has been developed allowing for the simultaneous examination of the soleus, peroneal, and tibialis anterior motoneuron pools elicited from a single peripheral stimulus. In order for this protocol to be useful, the reliability of the measures must be established. The purpose of the current study was to determine the intersession reliability of the soleus, peroneal, and tibialis anterior H-reflexes and their corresponding M-waves elicited from a single stimulus to the sciatic nerve. Ten healthy neurologically sound individuals (age: 23 +/- 7 yrs; height: 175 +/- 12 cm; mass: 76 +/- 22 kg) volunteered to participate in this investigation. To obtain the measurements, the sciatic nerve was stimulated just prior to its bifurcation into the tibial and common peroneal nerves in the popliteal fossa. A 1-ms square wave pulse was delivered in 0.2 V increments until the maximum M wave was seen in each muscle. The maximum H-reflex and M-waves were collected from each muscle and their ratios calculated. Intersession reliability over 2 consecutive days was estimated using intraclass correlation coefficients (ICC [2.1]). Intersession reliability for the soleus Max H, Max M, and H:M ratio were 0.9953, 0.9514, and 0.9747, respectively. The peroneal reliability measurements were as follows: 0.9979 (Max H), 0.9924 (Max M), and 0.9664 (H:M ratio). Intersession reliability was 0.8591, 0.9968, and 0.7810 for the tibialis anterior Max H. Max M. and H:M ratio, respectively. These results indicate that the H-reflex measured from the soleus, peroneal, and tibialis anterior musculature elicited with a single peripheral stimulus to the sciatic nerve is reliable between sessions. This protocol allows the clinician/researcher to reliably investigate the alpha motoneuron excitability of multiple motoneuron pools about the ankle at a single point in time.

Efficacy of Prophylactic Ankle Support: An Experimental Perspective.

OBJECTIVE: To provide a comprehensive review of the literature regarding the role of external ankle support on joint kinematics, joint kinetics, sensorimotor function, and functional performance. DATA SOURCES: We searched MEDLINE and SPORT Discus databases from 1960-2001 for the key words ankle bracing, ankle support, ankle taping, and ankle prophylaxes. We also used personal libraries based on our own research to complement the existing literature. DATA SYNTHESIS: The effects of external ankle support have been studied on a plethora of dependent measures. Here, we specifically discuss the role of external ankle support on joint kinematics, joint kinetics, sensorimotor function, and functional performance and present a general consensus regarding the overall effects of these prophylactic devices. CONCLUSIONS/RECOMMENDATIONS: The effects of ankle support on joint kinematics during static joint assessment and on traditional functional-performance measures (ie, agility, sprint speed, vertical jump height) are well understood. However, the potential effects of ankle support on joint kinetics, joint kinematics during dynamic activity (eg, a cutting maneuver), and various sensorimotor measures are not well known. Future research investigating the role of external ankle bracing needs to focus on these areas.

The Spectral Qualities of Postural Control are Unaffected by 4 Days of Ankle-Brace Application.

OBJECTIVE: To determine if the spectral qualities of medial-lateral (ML) and anterior-posterior (AP) center of pressure during a 1-legged stance are affected by 4 days of ankle-brace application. DESIGN AND SETTING: The study, which consisted of a pretest-posttest randomized group design, took place in the Sports Injury Research Laboratory at Indiana State University. SUBJECTS: Twenty-eight Indiana State University students, who had not suffered from any ankle injuries within the past 2 years and were free of any neurologic or vestibular disorders, participated in the study. MEASUREMENTS: The effects of 3 independent variables on mean frequency amplitude for both ML and AP center of pressure were examined: (1) treatment (brace, control), (2) frequency bin (0%-20%, 20%-40%, 40%-60%, 60%-80%, and 80%-100% of area), and (3) time (pretest, immediately after brace application, and after 1, 2, 3, or 4 days of brace wear). RESULTS: We detected no difference (P >.05) for the ML or AP mean frequency when comparing the brace and control groups. CONCLUSIONS: Application of an ankle brace may not require modifications in the postural-control strategies during a 1-legged stance in subjects with healthy ankles.