Tyler N. Brown

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.

Sex and limb differences in hip and knee kinematics and kinetics during anticipated and unanticipated jump landings: implications for anterior cruciate ligament injury

Objectives: In this study, the effects of temporal changes in unanticipated (UN) prelanding stimuli on lower limb biomechanics and the impact of sex and limb dominance on these variables during single-leg landings were determined. It was hypothesised that reductions in the time of prelanding UN stimuli, female sex, and the non-dominant limb would significantly increase high-risk landing biomechanics during UN jump landings. Methods: 26 (13 men and 13 women) had initial contact (IC) and peak stance (0–50%) phase (PS) lower limb joint kinematics and kinetics quantified during anticipated (AN) and UN single-leg (left and right) landings. Postlanding jump direction was governed via one of two randomly ordered light stimuli, presented either before initiation of the jump (AN), or 600 ms (UN1), 500 ms (UN2) or 400 ms (UN3) immediately before ground contact. Results: Statistically significant (p<0.05) differences in IC hip posture and PS hip and knee internal rotation moments occurred in UN compared with AN landings. Differences were not observed, however, among UN conditions for any biomechanical comparisons. Significant (p<0.05) differences in specific IC and PS hip and knee postures and loads occurred between sexes and limbs. Neither of these factors, however, influenced movement condition effects. Conclusion: UN landings induce modifications in landing biomechanics that may increase anterior cruciate ligament injury risk in both men and women. These modifications, however, do not appear overly sensitive to the timing of the UN stimulus, at least within a temporal range affording a successful movement response. Expanding UN training to include even shorter stimulus-response times may promote the additional central control adaptations necessary to manoeuvre safely within the random sports setting.

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.

Comparative adaptations of lower limb biomechanics during unilateral and bilateral landings after different neuromuscular-based ACL injury prevention protocols.

Abstract Brown, TN, Palmieri-Smith, RM, and McLean, SG. Comparative adaptations of lower limb biomechanics during unilateral and bilateral landings after different neuromuscular-based ACL injury prevention protocols. J Strength Cond Res 28(10): 2859–2871, 2014—Potentially valuable anterior cruciate ligament (ACL) injury prevention strategies are lengthy, limiting training success. Shorter protocols that achieve beneficial biomechanical adaptations may improve training effectiveness. This study examined whether core stability/balance and plyometric training can modify female landing biomechanics compared with the standard neuromuscular and no training models. Forty-three females had lower limb biomechanics analyzed during unilateral and bilateral landings immediately before and after a 6-week neuromuscular or no training programs. Sagittal and frontal plane hip and knee kinematics and kinetics were submitted to 3-way repeated-measures analyses of variance to test for the main and interaction effects of training group, landing type, and testing time. Greater peak knee flexion was evident in the standard neuromuscular group following training, during both bilateral (p = 0.027) and unilateral landings (p = 0.076 and d = 0.633). The plyometric group demonstrated reduced hip adduction (p = 0.010) and greater knee flexion (p = 0.065 and d = 0.564) during bilateral landings following training. The control group had significant reduction in peak stance knee abduction moment (p = 0.003) posttraining as compared with pretraining. The current outcomes suggest that significant biomechanical changes are possible by an isolated plyometric training component. The benefits, however, may not be evident across all landing types, seemingly limited to simplistic, bilateral landings. Integrated training protocols may still be the most effective training model, currently improving knee flexion posture during both bilateral and unilateral landings following training. Future prevention efforts should implement integrated training protocols that include plyometric exercises to reduce ACL injury risk of female athletes.

Associations between lower limb muscle activation strategies and resultant multi-planar knee kinetics during single leg landings

OBJECTIVES Anterior cruciate ligament injury prevention programs purportedly improve knee joint loading through beneficial modification of lower limb neuromuscular control strategies and joint biomechanics, but little is known about how these factors relate during single-legged landings. Thus, we examined the relationship between explicit lower limb muscular pre-activity patterns and knee joint biomechanics elicited during such landings. DESIGN Randomized controlled trial. METHODS Thirty-five female athletes had 3D knee joint biomechanics and lower limb EMG data recorded during a series of single-leg landings. Regression analysis assessed the relationship between pre-activity of vastus lateralis, lateral hamstring and rectus femoris with peak knee flexion angle and moment, and external anterior tibial shear force. Vastus lateralis, lateral hamstring and vastus lateralis:lateral hasmtring co-contraction assessed the relationship with knee abduction angle and moment. RESULTS Greater pre-activity of rectus femoris predicted increased peak anterior tibial shear force (R(2)=0.235, b=2.41 and P=0.003) and reduced knee flexion moment (R(2)=0.131, b=-0.591, and P=0.032), while greater lateral hamstring predicted decreased peak knee flexion angle (R(2)=0.113, b=8.96 and P=0.048). No EMG pre-activity parameters were predictors (P>0.05) for knee abduction angle and moment. CONCLUSIONS Current outcomes suggest reducing reliance on quadriceps activation may be beneficial during single-legged landings. It also, however, may be required for adequate joint stability during such maneuvers. Further research is needed to determine if inadequate hamstring activation, rather than elevated quadriceps activation, leads to hazardous loading during single-legged landings.