The influence of patellofemoral pain on muscle coordination, segment coordination, and segment coordination variability in runners

Management of patellofemoral pain syndrome (PFPS) remains a significant challenge in clinical practice and there is a need to understand the mechanisms for altered gait and muscular function which may lead to poor patient outcomes. The overall aim of the three studies in this dissertation was to determine if runners with current PFPS adapt their gait and muscle activation as a result of long-term, daily pain and/or in response to an acute pain flare and exertion during a moderate intensity 21-minute treadmill run compared to healthy controls. In addition, a resolved, asymptomatic PFPS group was included to investigate potential mechanisms for the frequent reoccurrence of pain experienced by those with a history of PFPS. The lack of differences in baseline kinematic, segment coordination, and segment coordination variability measures suggest that there are no long-term gait adaptations to pain in either injury group that manifest as resultant gait patterns. Several differences were identified in baseline kinetics among all three groups for peak hip abduction and external rotation as well as ankle inversion moments. These findings indicate that: 1) runners with a history of PFPS have different loading patterns at the hip and ankle compared to healthy runners and 2) these altered loading patterns are not substantial enough to alter resultant kinematic patterns of movement. In addition to these joint moments, altered muscle coordination discriminated between all three groups. These findings have significant implications for identifying individuals at risk of re-injury and helping to improve treatment efficacy in runners with PFPS. Movement evoked pain is a primary characteristic of PFPS, and the treadmill run used in these studies was sufficient to cause a pain response in the injured group. Changes seen in the outcome measures of the three studies at the end of the run are indicative of a response to a combination of increased pain and exertion. Greater anti-phase motion of the sagittal thigh-transverse shank in the injured group compared to controls suggests that altered movement control about the knee may be related to increased pain in those with PFPS. In addition to the decreased coordination variability observed in those with PFPS, there were also differences in coordination variability between the resolved and control groups, with the resolved group often showing increases in variability compared to controls. This suggests that abnormal movement flexibility may persist even once painful symptoms are resolved and that individuals with a history of PFPS do not return to healthy gait patterns following resolution of symptoms

Does Footfall Pattern in Forefoot Runners Change Over a Prolonged Run?

There has been much debate on the benefits of a forefoot versus rearfoot strike pattern in distance running in terms of performance and injury prevalence. Shock attenuation occurs more prominently in soft tissues at impact in forefoot runners compared to the passive skeletal loading in rearfoot runners. Recent studies indicate that a forefoot strike pattern may not be maintainable over long distance efforts. Therefore, this study tested the hypothesis that habitual forefoot runners could not maintain their strike pattern throughout a prolonged, intensive run. Fourteen forefoot runners ran to voluntary exhaustion on an instrumented force treadmill (average run duration: 15.4±2.2 minutes). Kinematic and kinetic data were sampled each minute at 200Hz and 1000Hz, respectively. Ankle plantar-flexor torque was measured during pre- and post-run isometric contractions, during which electromyographic activity was measured in the soleus, lateral, and medial gastrocnemius. Loading rate (49.95±14.83 to 57.40±22.53 BW*s-1, p=0.0311) and impact peak (1.35±0.43 to 1.50±0.51, p=0.0207) increased significantly throughout the run. Both peak knee flexion (-33.93±3.67º to -36.21±3.48º, p=\u3c0.0000) and sagittal ankle angle at touchdown (-11.83±5.33º to -9.33±6.29º, p =0.0202) increased significantly. Ankle torque decreased significantly from pre- to post-run (120.57±33.57 to 110.76±32.91 Nm, p = 0.0154). This was accompanied by a decrease in medial and lateral gastrocnemius integrated electromyographic activity (iEMG) (p=0.0387 and 0.0186, respectively). The results indicated that there were significant changes in landing mechanics in the habitual forefoot runners with increased levels of exertion, as they shifted towards strike patterns more similar to rearfoot runners throughout the run. These changes are in line with metabolic findings of other studies. There is increased eccentric loading of the ankle plantar-flexor muscles at touchdown in forefoot runners that may contribute to a decreased torque output by the end of the run. The decline in iEMG may indicate altered central drive of the system and a decline in the impact attenuation ability of the triceps surae, leading to the changes exhibited up the kinematic chain. These findings suggest that while forefoot strike patterns are good for speed, the onset of fatigue may affect the ability to maintain this pattern during a prolonged, intensive effort

Which is the primary factor influencing running stride parameters: age or lower limb strength?

Much still remains unknown about the impact of age, and age-related changes in muscle function, on gait parameters. The aim of this study was to examine the impact of strength on running gait parameters across the adult lifespan. We tested the hypothesis that a greater amount of the variance in peak hip, knee and ankle sagittal plane moments would be explained by peak isometric joint torques as compared to age. Twenty-four healthy adults, ages 20-66 years, completed 5 trials on an overground 20-meter runway at a standardized velocity of 3.5 ms-1 (± 5%). Participants performed maximal isometric plantar flexion and knee extension for three contractions lasting three seconds each. Linear regression analysis between strength, age, and moments were performed. At the ankle, age alone explained 14.4% of the variance in the peak ankle joint moment. There was not a significant increase in the variance explained when strength was added to the model. At the knee, neither age nor strength explained a significant portion of the variance in peak knee moments. However, together age and strength explained 27.9% of the variance in the peak knee moment. No significant associations were found between the hip moments and either knee and ankle strength. These results suggest that other age-related physiological changes may drive changes in gait mechanics more so than maximal torque production. A more dynamic measure of muscle function, such as power or isokinetic torque at varying speeds may have greater predictive value for gait performance

COORDINATIVE VARIABILITY IN FOREFOOT RUNNERS DURING AN EXHAUSTIVE RUN

The purpose of this study was to investigate the effects of a prolonged run on coordinative variability and how it relates to impact dynamics in forefoot runners during an exhaustive run. Thirteen individuals ran on an instrumented treadmill and were instructed to select a pace they can maintain for at least 15 minutes but no longer than 20 minutes. A post hoc analysis revealed two subgroups emerged. Eight individuals were able to maintain a forefoot striking pattern throughout the run (NCG: no change group), while the remaining five moved to a more rearfoot strike (CG: change group). The results demonstrated that the impact characteristics changed for the CG only. This was accompanied by changes in CV, suggesting that individuals reorganize their degrees of freedom as they fatigue. The reorganization of footfall patterns may represent an adaptation to meet energy requirements to complete the task

LOWER EXTREMITY COORDINATION VARIABILITY DURING ANTICIPATED AND UNANTICIPATED SIDESTEPPING: IMPLICATIONS FOR ACL INJURY PREVENTION

Non-contact anterior cruciate ligament (ACL) injuries commonly occur during sidestepping, particularly under time constraints. This study investigated the differences in lower limb coordination variability (CV) of five male team sport athletes during anticipated and unanticipated sidestepping. Intra-limb couplings associated with ACL injury mechanisms were investigated. Athletes demonstrated 21% greater thigh rot/leg rot CV; 31% greater thigh abd-add/leg abd-add CV; 22% greater knee flex-ext/hip rot CV and 14% greater hip rot/knee abd-add CV during unanticipated sidestepping. These results suggest that CV increases as a function of task complexity. Consequently, injury prevention programs must incorporate perceptual components in order to optimise planning time and coordinate appropriate postural adjustments to counter external loads

MUSCLE ACTIVATION STRATEGIES DURING AN UNANTICIPATED STOPPING TASK

The purpose of this study was to determine how time constraints during stopping in sports affect lower limb muscle activation strategies in both the termination and stability steps. Rapid deceleration is common in both recreational and professional sport and has previously been associated with lower limb injury. To investigate control differences between anticipated and unanticipated stopping, total muscle activation and directed cocontraction ratios were used to analyse lower limb muscle activation. Increased plantar flexor and knee flexor activity was found during the pre-contact and weight acceptance phases of unanticipated stopping compared with anticipated stopping. These results support the hypothesis that lower limb muscle activity is altered when the task is unanticipated, which may place athletes at higher risk of lower limb injury in sport

THE INFLUENCE OF PATELLOFEMORAL PAIN ON COORDINATION VARIABILITY OVER A PROLONGED TREADMILL RUN

The purpose of this study was to understand the influence of patellofemoral pain on lower extremity segment coordination variability throughout a 21-minute treadmill run. Couplings between the pelvis, thigh, and shank were compared at the beginning and end of the run between healthy and injured runners. Average coordination variability in weight acceptance and mid-stance was increased in healthy runners over the course of the run and decreased in those experiencing pain. These results support the hypothesis that injured runners experiencing pain may not be as flexible to internal and external perturbations compared to their healthy counterparts. Thus, in the presence of pain, these runners may place greater stress on specific lower extremity tissues leading to greater risk for injury at these sites

COORDINATION VARIABILITY IN OVERGROUND RUNNING AND WALKING AT PREFERRED AND FIXED SPEEDS

Coordination variability (CoordV) is impacted by the type and speed of locomotion, however, the appropriate number of trials required for stable outputs during overground locomotion is yet to be determined. The purpose of this study was to analyse the CoordV of lower limb segment and joint couplings to determine the number of trials needed for a stable mean during running and walking at preferred and fixed speeds. Three-dimensional lower-limb kinematics were captured for recreational runners (n = 10) performing 20 trials of each condition. Using a modified vector coding technique, segment and joint couplings were derived, from which, CoordV was calculated using circular statistics. The number of trials required to achieve a mean within 100±10% of a 20 stride mean was determined for each individual. The study findings indicate the need for between 8 and 9 trials to produce a stable mean and contribute to reliable biomechanical outputs

Who works for whom and the UK gender pay gap?

This study reports novel facts about the UK gender pay gap. We use a large, longitudinal, representative and employer employee linked dataset for the years 2002-16. Men’s average log hourly wage was 22 points higher than women’s in this period. We ask how much of this gap is accounted for by the differences in whom men and women worked for; how much is explained by the relative wage premiums that firms paid their employees, after adjusting for the influence of other factors, such as occupations and tenure? The answer is less than 1 percentage point, or about one eighteenth of the adjusted hourly gender pay gap. We also find that the allocation of men and women to occupations was as unimportant as how workers were allocated to firms. These results show that in the United Kingdom what happens within firms and occupations is far more important than what jobs men and women have. Therefore, attention should focus on why men and women within UK firms tend to receive different rates of pay

Who works for whom and the UK gender pay gap?

This study reports novel facts about the UK gender pay gap. We use a large, longitudinal, representative and employer employee linked dataset for the years 2002-16. Men’s average log hourly wage was 22 points higher than women’s in this period. We ask how much of this gap is accounted for by the differences in whom men and women worked for; how much is explained by the relative wage premiums that firms paid their employees, after adjusting for the influence of other factors, such as occupations and tenure? The answer is less than 1 percentage point, or about one eighteenth of the adjusted hourly gender pay gap. We also find that the allocation of men and women to occupations was as unimportant as how workers were allocated to firms. These results show that in the United Kingdom what happens within firms and occupations is far more important than what jobs men and women have. Therefore, attention should focus on why men and women within UK firms tend to receive different rates of pay