Full length ArticleLower limb control and strength in runners with and without patellofemoral pain syndrome
Introduction
Overuse injuries are frequent in recreational runners, with a reported annual prevalence of up to 70% [1]. Patellofemoral pain syndrome (PFPS), described as anterior or retropatellar knee pain or pain along the lateral and medial borders of the patella [2], is the most common running injury with 17% of diagnoses [3]. Several factors have been suggested to explain the presence of PFPS including decreased muscle strength and altered mechanical loading, lower limb kinematics, and muscle activation patterns during running.
Mechanical overload is recognized as a risk factor for the development of running-related injuries [4]. Specifically in the patellofemoral joint, running induces repetitive compressive forces of up to 4.5 times the bodyweight [5]. It has been suggested by Davis et al. that runners with PFPS show higher vertical loading rates of ground reaction forces during early stance [6], which have been linked with increased patellofemoral joint forces [7].
Considering the high impact forces during running, it can be hypothesized that impaired lower limb muscle strength, or kinematics and muscle activation patterns during running should facilitate the development of PFPS [8]. Several studies have looked at these factors in runners with PFPS. For muscle strength, various findings have been reported: while cross-sectional studies reported decreased knee extensors [9] or hip abductors strength [10], [11], two prospective studies found either no difference [12] or increased abductor/adductor and decreased external/internal rotator strength ratios between runners who would eventually develop PFPS and those who would not [13]. Thus, onset of PFPS in runners may not necessarily be causally related to strength deficits.
Regarding running kinematics, different results were found in female and male runners. Female runners with PFPS show increased hip adduction (HADD) and hip internal rotation (HIR) during stance compared to controls [14], [15]. In contrast, male runners with PFPS exhibit increased contralateral pelvic drop (CPD) and HADD [16], or even increased hip abduction [17] during stance in comparison to controls. However, most of these studies did not concurrently assess muscle activation patterns to determine the mechanisms underlying such kinematic deficits. The only study to do so found delayed and shorter duration of gluteus medius (GMed) activation during the stance phase in female runners [18]. In addition, increased peak angles of HADD and HIR were correlated with delayed onset of GMed and gluteus maximus (GMax).
To our knowledge, no study has simultaneously looked at muscle strength, lower limb kinematics, muscle activations and ground reaction forces (GRF) during running in this population. The simultaneous study of all of these factors is warranted to enhance our understanding of the mechanisms underlying altered lower limb control during running. Most studies described above have specifically recruited rearfoot strikers, even though PFPS also develops in midfoot and forefoot strikers. Furthermore, standardized cushioned neutral running shoes were used in most of these studies; thus, data were collected in conditions different from the runner's typical training environment. The objective of the present study was to compare lower limb kinematics, muscle activation patterns and GRF during treadmill running, as well as lower limb strength, in recreational runners with or without PFPS regardless of foot strike pattern or footwear. We hypothesized that runners with PFPS would exhibit greater GRF, a combination of increased peak HADD, HIR and/or CPD angles and decreased activation of GMed during the stance phase of running, without concomitant strength deficits.
Section snippets
Participants
Twenty-one recreational runners with PFPS (PFPS group) and 20 runners without PFPS (Control group), matched for age, sex and foot strike pattern, were recruited (Table 1). All participants: (1) were aged between 18 and 45, (2) ran at least 15 km per week prior to enrolment, (3) had no history of rheumatoid, inflammatory or neurological disease, surgery to the lower limbs, patellar dislocation or ligamentous injury, and (4) had no other current injury to the lower limbs. Runners with PFPS were
Results
Both groups were similar in terms of gender, age, height, weight, weekly running distance, shoe type, foot strike pattern, and step frequency during running (P > 0.16; Table 1). Muscle strength (% of bodyweight) was not statistically different across groups (P > 0.35; Table 1).
Discussion
To our knowledge, this is the first study to concurrently compare lower limb muscle activations, kinematics and GRF during treadmill running as well as muscle strength in runners with and without PFPS. When pooling all of our participants, regardless of gender or foot strike pattern, no between-group differences were found in variables that have been previously associated with PFPS in runners. However, significant differences were observed in subgroups of females and RFS. Our hypothesis
Conclusion
In conclusion, no significant differences were found in lower limb strength, peak angles of HADD, HIR, or CPD, muscle activity of GMax, GMed, VMO, or VL or GRF between recreational runners with and without PFPS. Only longer duration of SOL activity and increased HADD during late stance were found in runners with PFPS. However, sub-analyses revealed gender- and foot strike-specific differences such as decreased GMed activity and lower VGRF in RFS with PFPS. Therefore, PFPS in runners may not
Conflict of interest
The authors do not have any conflict of interest to report.
Funding sources
This research project was supported by the Ordre professionnel de la physiothérapie du Québec (OPPQ). The funding source was not involved in the study's design, conduct or reporting. J.F.E. was supported by a scholarship from the Fonds de recherche du Québec - Santé (FRQ-S). J.S.R. was supported by a salary award from the FRQ-S.
Acknowledgements
The Authors would like to thank all runners who volunteered to participate in this study, as well as Mr. Guy St-Vincent, eng., MSc for his help in data collection and analysis.
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