Mark A. Lyle

The Effects of Isolated Hip Abductor and External Rotator Muscle Strengthening on Pain, Health Status, and Hip Strength in Females With Patellofemoral Pain: A Randomized Controlled Trial

STUDY DESIGN Randomized controlled trial. OBJECTIVES To examine the effectiveness of isolated hip abductor and external rotator strengthening on pain, health status, and hip strength in females with patellofemoral pain (PFP). BACKGROUND Altered hip kinematics resulting from hip muscle weakness has been proposed as a contributing factor in the development of PFP. To date, no study has examined clinical outcomes associated with isolated hip muscle strengthening in those with PFP. METHODS Twenty-eight females with PFP were sequentially assigned to an exercise (n = 14) or a no-exercise control group (n = 14). The exercise group completed bilateral hip abductor and external rotator strengthening 3 times per week for 8 weeks. Pain (visual analog scale), health status (WOMAC), and hip strength (handheld dynamometer) were assessed at baseline and postintervention. Pain and health status were also evaluated at 6 months postintervention in the exercise group. Two-factor mixed-model analyses of variance were used to determine the effects of the intervention on each outcome variable. RESULTS Significant group-by-time interactions were observed for each variable of interest. Post hoc testing revealed that pain, health status, and bilateral hip strength improved in the exercise group following the 8-week intervention but did not change in the control group. Improvements in pain and health status were sustained at 6-month follow-up in the exercise group. CONCLUSION A program of isolated hip abductor and external rotator strengthening was effective in improving pain and health status in females with PFP compared to a no-exercise control group. The incorporation of hip-strengthening exercises should be considered when designing a rehabilitation program for females with PFP. LEVEL OF EVIDENCE Therapy, level 2b.

Neural Regulation of Limb Mechanics: Insights from the Organization of Proprioceptive Circuits

Sensory feedback arising from muscle spindle receptors and Golgi tendon organs are known to influence limb mechanics during postural and locomotor tasks. The purpose of this chapter is to synthesize data concerning the organization and actions of these proprioceptive pathways, and then to propose how current models can be used to promote understanding of their functional role in regulating whole limb stiffness. Following a historical introduction, the role of length feedback in transforming the mechanical properties of muscles into more spring-like actuators is reviewed. Next, we describe the organization of intermuscular length and force feedback circuits in the context of the mechanical interrelationships of the muscles involved. Finally, we provide a conceptual framework for understanding the role of proprioceptive feedback in the regulation of limb mechanics across a continuum of behaviors, and show how a developing computational model can be used to understand how these pathways are integrated to regulate limb stiffness. We conclude from a qualitative appraisal of the data that intermuscular length feedback reinforces the mechanical relationships between antagonists and between synergistic muscles that cross the same or different joints. Furthermore, inhibitory force feedback is organized to manage the distribution of stiffness across joints as well as intersegmental dynamics due to the inertial properties of the limb segments.

Lower extremity dexterity is associated with agility in adolescent soccer athletes

Agility is important for sport performance and potentially injury risk; however, factors affecting this motor skill remain unclear. Here, we evaluated the extent to which lower extremity dexterity (LED) and muscle performance were associated with agility. Fourteen male and 14 female soccer athletes participated. Agility was evaluated using a hopping sequence separately with both limbs and with the dominant limb only. The LED test evaluated the athletes’ ability to dynamically regulate foot–ground interactions by compressing a spring prone to buckling with the lower limb. Muscle performance included hip and knee isometric strength and vertical jump height. Correlation analyses were used to assess the associations between muscle performance, LED, and agility. Multiple regression models were used to determine whether linear associations differed between sexes. On average, the female athletes took longer to complete the agility tasks than the male athletes. This difference could not be explained by muscle performance. Conversely, LED was found to be the primary determinant of agility (double limb: R2 = 0.61, P < 0.001; single limb: R2 = 0.63, P < 0.001). Our findings suggest that the sensorimotor ability to dynamically regulate foot–ground interactions as assessed by the LED test is predictive of agility in soccer athletes. We propose that LED may have implications for sport performance, injury risk, and rehabilitation.

The lower extremity dexterity test as a measure of lower extremity dynamical capability

The capability of the lower extremity to dynamically interact with the ground is important for skilled locomotor performance. However, there is currently no test method designed to specifically quantify this sensorimotor ability, which we refer to as lower extremity dexterity. We describe a new method to quantify lower extremity dexterity, examine its reliability (n=10), and evaluate the extent to which it is associated with lower extremity strength and anthropometry in healthy young adults (n=38). The lower extremity dexterity test (LED-test)-an adaptation of the Strength-Dexterity test for the fingers-consists of using the isolated lower extremity to compress a slender spring prone to buckling at low forces. The goal of the LED-test is to sustain the highest compression force possible. Applying higher forces makes the spring increasingly unstable, thus achieving higher compression forces represents better ability to dynamically control instability at low force levels. As such, the LED-test provides a novel way to quantify the capability of the lower extremity to regulate dynamic and unstable foot-ground interactions at submaximal forces. LED-test performance ranged between 88.6 and 119.6N, test-retest reliability was excellent (ICC(2,3)=0.94), and the minimal detectable difference was 5.5N. Performance was not correlated with strength or height (r(2)≤0.053, p>0.05), and only weakly with body mass (r(2)=0.116, p=0.04). We propose that the unique lower extremity capability quantified by the LED-test could be informative of skilled locomotor performance and injury risk.

Influence of maturation on instep kick biomechanics in female soccer athletes.

PURPOSE The purpose of this study was to compare kicking biomechanics between young female soccer players at two different stages of physical maturation and to identify biomechanical predictors of peak foot velocity. METHODS Swing and stance limb kinematics and kinetics were recorded from 20 female soccer players (10 prepubertal, 10 postpubertal) while kicking a soccer ball using an angled two-step approach. Peak foot velocity as well as hip and knee kinematics and kinetics were compared between groups using independent-samples t-tests. Pearson correlation coefficients and stepwise multiple regression were used to identify predictors of peak foot velocity. RESULTS Peak foot velocity and the peak swing limb net hip flexor moment was significantly greater in the postpubertal group when compared with the prepubertal group (13.4 vs 11.6 m·s(-1), P = 0.003; 1.22 vs 1.07 N·m·kg(-1)·m(-1), P = 0.03). Peak stance limb hip and knee extensor moments were not different between groups. Although the peak swing limb hip and knee flexion angles were similar between groups, the postpubertal group demonstrated significantly less peak stance limb hip and knee flexion angles when compared with the prepubertal group (P < 0.001 and P = 0.045). Using a linear regression model, swing limb peak hip flexor moment and peak swing limb hip extension range of motion combined to explain 65% of the variance in peak foot velocity. CONCLUSIONS Despite a difference in stance limb kinematics, similar swing limb kinematics between groups indicates that the prepubertal female athletes kicked with a mature swing limb kick pattern. The ability to generate a large hip flexor moment of the swing limb seems to be an important factor for improving kicking performance in young female soccer players.

Patterns of intermuscular inhibitory force feedback across cat hindlimbs suggest a flexible system for regulating whole limb mechanics

Prior work has suggested that Golgi tendon organ feedback, via its distributed network linking muscles spanning all joints, could be used by the nervous system to help regulate whole limb mechanics if appropriately organized. We tested this hypothesis by characterizing the patterns of intermuscular force-dependent feedback between the primary extensor muscles spanning the knee, ankle, and toes in decerebrate cat hindlimbs. Intermuscular force feedback was evaluated by stretching tendons of selected muscles in isolation and in pairwise combinations and then measuring the resulting force-dependent intermuscular interactions. The relative inhibitory feedback between extensor muscles was examined, as well as symmetry of the interactions across limbs. Differences in the directional biases of inhibitory feedback were observed across cats, with three patterns identified as points on a spectrum: pattern 1, directional bias of inhibitory feedback onto the ankle extensors and toe flexors; pattern 2, convergence of inhibitory feedback onto ankle extensors and mostly balanced inhibitory feedback between vastus muscle group and flexor hallucis longus, and pattern 3, directional bias of inhibitory feedback onto ankle and knee extensors. The patterns of inhibitory feedback, while different across cats, were symmetric across limbs of individual cats. The variable but structured distribution of force feedback across cat hindlimbs provides preliminary evidence that inhibitory force feedback could be a regulated neural control variable. We propose the directional biases of inhibitory feedback observed experimentally could provide important task-dependent benefits, such as directionally appropriate joint compliance, joint coupling, and compensation for nonuniform inertia. NEW & NOTEWORTHY Feedback from Golgi tendon organs project widely among extensor motor nuclei in the spinal cord. The distributed nature of force feedback suggests these pathways contribute to the global regulation of limb mechanics. Analysis of this network in individual animals indicates that the strengths of these pathways can be reorganized appropriately for a variety of motor tasks, including level walking, slope walking, and landing.

Musculotendon adaptations and preservation of spinal reflex pathways following agonist‐to‐antagonist tendon transfer

Tendon transfer surgeries are performed to restore lost motor function, but outcomes are variable, particularly those involving agonist‐to‐antagonist muscles. Here, we evaluated the possibility that lack of proprioceptive feedback reorganization and musculotendon adaptations could influence outcomes. Plantaris‐to‐tibialis anterior tendon transfer along with resection of the distal third of the tibialis anterior muscle belly was performed in eight cats. Four cats had concurrent transection of the deep peroneal nerve. After 15–20 weeks, intermuscular length and force‐dependent sensory feedback were examined between hindlimb muscles, and the integrity of the tendon‐to‐tendon connection and musculotendon adaptations were evaluated. Three of the transferred tendons tore. A common finding was the formation of new tendinous connections, which often inserted near the original location of insertion on the skeleton (e.g., connections from plantaris toward calcaneus and from tibialis anterior toward first metatarsal). The newly formed tissue connections are expected to compromise the mechanical action of the transferred muscle. We found no evidence of changes in intermuscular reflexes between transferred plantaris muscle and synergists/antagonists whether the tendon‐to‐tendon connection remained intact or tore, indicating no spinal reflex reorganization. We propose the lack of spinal reflex reorganization could contribute the transferred muscle not adopting the activation patterns of the host muscle. Taken together, these findings suggest that musculotendon plasticity and lack of spinal reflex circuitry reorganization could limit functional outcomes after tendon transfer surgery. Surgical planning and outcomes assessments after tendon transfer surgery should consider potential consequences of the transferred muscles intermuscular spinal circuit actions.