The effects & mechanisms of increasing running step rate: A feasibility study in a mixed-sex group of runners with patellofemoral pain

Highlights

• Recruitment and retention of a mixed sex sample of runners with PFP was feasible.

• Increasing running step rate by 7.5% improved PFP symptoms at short-term follow up.

• Peak hip internal rotation, hip adduction and knee flexion were reduced post-retraining.

• No muscle function mechanisms, investigated using sEMG, were identified.

Abstract

Objectives

To explore feasibility of recruitment and retention of runners with patellofemoral pain (PFP), before delivering a step rate intervention.

Design

Feasibility study.

Setting

Human performance laboratory.

Participants

A mixed-sex sample of runners with PFP (n = 11).

Main outcome measures

Average/worst pain and the Kujala Scale were recorded pre/post intervention, alongside lower limb kinematics and surface electromyography (sEMG), sampled during a 3 KM treadmill run.

Results

Recruitment and retention of a mixed-sex cohort was successful, losing one participant to public healthcare and with kinematic and sEMG data lost from single participants only. Clinically meaningful reductions in average (MD = 2.1, d = 1.7) and worst pain (MD = 3.9, d = 2.0) were observed. Reductions in both peak knee flexion (MD = 3.7°, d = 0.78) and peak hip internal rotation (MD = 5.1°, d = 0.96) were observed, which may provide some mechanistic explanation for the identified effects. An increase in both mean amplitude (d = 0.53) and integral (d = 0.58) were observed for the Vastus Medialis Obliqus (VMO) muscle only, of questionable clinical relevance.

Conclusions

Recruitment and retention of a mixed sex PFP cohort to a step rate intervention involving detailed biomechanical measures is feasible. There are indications of both likely efficacy and associated mechanisms. Future studies comparing the efficacy of different running retraining approaches are warranted.

Introduction

Recreational running positively influences cardiac (Petrovic-Oggiano, Damjanov, Gurinovic, & Glibetic, 2010), metabolic (Williams, 2014) and mental (Ghorbani et al., 2014) health. Despite the reported benefits, recreational running is reported to bring about an increased risk of musculoskeletal pain (Saragiotto et al., 2014; van Gent et al., 2007). Overall incidence of musculoskeletal pain amongst recreational runners ranges from 19% to 94% (van Gent et al., 2007), with patellofemoral pain (PFP) thought to be the most common (Taunton et al., 2002). Specific annual incidence of PFP amongst recreational runners ranges from 4% to 21%, (Noehren, Hamill, & Davis, 2013; Ramskov, Barton, Nielsen, & Rasmussen, 2015; Thijs, Van Tiggelen, Roosen, De Clercq, & Witvrouw, 2007), with overall prevalence in sports medicine facilities suggested to be 17% (Taunton et al., 2002).

Running biomechanics has been reported to be a risk factor for, and associated with, running related PFP. Specifically, peak hip adduction during running has been reported to be significantly higher in female runners who develop subsequent PFP when compared to those who remain asymptomatic (Neal, Barton, Gallie, O'Halloran, & Morrissey, 2016; Noehren et al., 2013). In addition, based on our recent meta-analysis (Neal et al., 2016), peak hip adduction, peak hip internal rotation and contralateral pelvic drop are also significantly higher in runners with PFP when compared to asymptomatic controls. For neuromuscular function, females with PFP have been reported to have delayed gluteal muscle onset prior to foot contact and shorter gluteal muscle activation duration compared to asymptomatic controls (Willson, Kernozek, Arndt, Reznichek, & Scott Straker, 2011).

At present, evidence suggests that exercise interventions, whilst effective at reducing symptoms in runners with PFP in the short-term, do not result in full symptom resolution (Earl & Hoch, 2011; Ferber, Kendall, & Farr, 2011). Moreover, exercise may not derive its effects by way of a kinematic mechanism, as multiple studies have demonstrated that exercise programs designed to increase hip strength do not alter running kinematics reported to be associated with PFP (Earl & Hoch, 2011; Sheerin, Hume, & Whatman, 2012; Willy & Davis, 2011; Wouters et al., 2012). This brings into question the ability of an exercise intervention to provide long-term resolution to running related PFP, as it fails to target factors known to be associated with the development and persistence of the condition. It is this premise that originally led to the development of what has been termed running retraining (Heiderscheit, 2011), or more specifically ‘the implementation of any cue or strategy designed to alter an individual's running technique’ (I. Davis, 2005).

Reports from observational studies, involving visual and verbal cues to reduce peak hip adduction, indicates running retraining may reduce pain and improve function in female runners with PFP who demonstrate more than 20° peak hip adduction during running (Neal et al., 2016; Noehren, Scholz, & Davis, 2011; Willy, Scholz, & Davis, 2012). The key limitation of this work is that the results can only be extrapolated to a minority of runners with PFP (i.e. females with high peak hip adduction). In addition, a recently completed randomised controlled trial (RCT) has established efficacy for cues to transition from rearfoot to forefoot strike in combination with a load management running program in a mixed-sex, but again a predominantly female, cohort (Roper et al., 2016). The limitation of this study is that cues to transition to a forefoot strike are only applicable to those who rearfoot strike at baseline. Additionally, it is thought that such a change to running mechanics may also be injurious by virtue of the increase in Achilles tendon load that is observed with forefoot strike running compared to rearfoot strike running (Rice & Patel, 2017). This is reinforced by the fact that 25% (2/8) of the runners in this RCT who transitioned to a forefoot strike pattern reported ankle soreness at follow up (Roper et al., 2016).

It has been reported that cues to increase running step rate do not increase Achilles tendon load (Lyght, Nockerts, Kernozek, & Ragan, 2016) and thus may be a more widely applicable running retraining option to those previously studied. A recent feasibility study has reported that a step rate increase of 10% combined with running in a minimalist shoe was superior to foot orthoses at reducing pain and improving function at 12 week follow up in runners with PFP (Bonacci, Hall, Saunders, & Vicenzino, 2017). An increase in step rate of 10% has also been reported to favourably alter patellofemoral joint stress in both runners with PFP and asymptomatic runners, (Willson, Sharpee, Meardon, & Kernozek, 2014), though the actual reduction in step length reported was much greater (14%). In addition, no evaluation of symptoms could be reported in this study due to the limitation of the cross-sectional, observational design. Observational work in asymptomatic runners also indicates that more modest increases in running step rate of 5% or 7.5% may still reduce peak hip adduction (Heiderscheit, Chumanov, Michalski, Wille, & Ryan, 2011; Willy et al., 2015), albeit of a smaller magnitude.

A recent three-arm RCT (Esculier et al., 2017) found that a running retraining intervention to increase step rate was no more effective than education focused on load management, or compared to the same education combined with exercise therapy in runners with PFP. Whilst no treatment group had superior outcomes, the step rate intervention did result in significant reductions in both worst and running specific pain. All three groups remained symptomatic at the primary end point (20 weeks), and running-related pain was higher (2.5/10) in the step rate group compared to previous studies where hip adduction (0.5/10) (Noehren et al., 2011; Willy et al., 2012) and strike pattern (1.0/10) (Roper et al., 2016) has been targeted. This could be explained by the absence of a faded-feedback protocol to facilitate the retraining intervention (Irene Davis, 2017), which has been found to be effective by previous studies (Noehren et al., 2011; Roper et al., 2016; Willy et al., 2012).

The primary aim of this study was to investigate the feasibility of a pragmatic running retraining intervention, by cueing a 7.5% increase in running step rate using a faded feedback protocol. Specific objectives included (i) the recruitment of an appropriate number of both males and females from a clinical population and (ii) the collection of both symptom and function data to determine an estimate of the effects derived from the intervention. The secondary aim was to investigate the potential kinematic and muscle function mechanisms explaining any effects induced by the intervention.