January 2015

Implications of reduced stride length in running

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Decreasing stride length during running has been shown to result in biomechanical changes that are associated with reduced loading of biological tissues and, by extension, also may reduce the risk of injuries such as stress fractures, iliotibial band syndrome, and patellofemoral pain.

By Melissa A. Thompson, PhD, and Kristine M. Hoffman, DPM

Running is one of the most popular fitness activities, yet it is associated with a high incidence of lower extremity musculoskeletal injury. Injury rates as high as 79% have been reported in runners,1 with patellofemoral pain, iliotibial band syndrome, and stress fractures being some of the most commonly reported events.2 Given the high injury risk, numerous running technique alterations have been suggested in an effort to decrease injury rates.

One gait alteration that has been proposed to reduce running- related injury risk is reducing stride length. Decreasing stride length during running has been associated with several biomechanical changes that may underlie reduced injury rates. Further, there is evidence to suggest that reducing stride length during running may improve symptoms associated with certain clinical conditions, such as chronic exertional compartment syndrome, iliotibial band syndrome, and patellofemoral pain.

Overuse injuries are dependent on loading magnitude, type of load, and the number of loading cycles, as well as the health and condition of the relevant biological tissue.3 When running, the body’s mass is repeatedly decelerated, resulting in forces that travel through the musculoskeletal system. These forces are actively attenuated by eccentric activation of muscles crossing lower extremity joints4,5 and passively attenuated by structures such as the ground, shoe midsole, heel pad, articular cartilage, intervertebral discs, and menisci.6,7 The repetitive attenuation of impact forces during running is thought to contribute to overuse injuries.8-11 The magnitude of loading of biological tissue (eg, bone, tendon, ligament, and cartilage) during the impact phase of running is determined by the combined effects of the ground reaction forces (GRF), lower extremity kinematics, and muscle activation.12

Decreasing stride length

Decreasing stride length during running has been shown to result in several biomechanical changes that are associated with reduced loading of biological tissues and, by extension, also may be associated with reduced injury risk. Specifically, decreasing stride length has been shown to reduce GRFs, joint moments, impact accelerations, and leg stiffness, factors that have been associated with a greater risk of running-related injury.1,12,13

1running-iStock_000014151331Large-copyGRF magnitude provides an estimate of the forces that are transmitted to the musculoskeletal system during running. When running at moderate speeds the vertical component of the GRF has peak values approximately three times body weight.14 During running the vertical GRF often has two peaks, the impact peak that occurs at initial ground contact and the active peak that represents the forces at midstance. Research has shown that decreasing stride length decreases the impact peak15 and active peak of the vertical GRF,16-20 and has found that reducing stride length results in a decreased vertical loading rate of the GRF.15

There is evidence to suggest that greater vertical impact peaks and loading rates are associated with an increased incidence of tibial stress fractures21-24 and plantar fasciitis.25 Thus, decreasing stride length may help reduce these types of injury.

Joint moments represent the net effect of muscles and ligament acting across the joint, and are commonly used to assess joint loading during running. Increased stride length has been associated with greater ankle, knee, and hip joint moments.4,17,20,26 While re-search regarding the relationship between joint moments and running-related injuries is sparse, it is generally thought that higher joint moments increase risk for joint and other musculoskeletal injuries.

In addition to measuring GRFs and joint moments, loading on the body during running can be assessed by measuring accelerations caused by impact.27 Body segment acceleration is dependent on the GRF magnitude and the damping effects of the body’s passive and active shock absorbers.4 It has been suggested that greater impact accelerations result in increased prevalence of running-related injuries. Studies have shown that tibial accelerations decrease when stride length is reduced.4,28-30 This further suggests that decreasing stride length may reduce running-related injuries.

Lastly, decreasing stride length has been shown to alter leg stiffness, which may have implications for injury. The mechanics of running on the leg is often described as a spring supporting the body’s mass. The musculoskeletal system can alter the stiffness of this spring system, and research has shown that decreasing stride length reduces leg stiffness.16,18 It appears likely that there is an ideal level of leg stiffness that minimizes injury risk, with increased stiffness associated with bony injuries and decreased stiffness associated with soft tissue injuries.31

Further, barefoot running, which typically results in decreased stride length, has also been associated with reduced GRFs and joint moments.32 Thompson et al had individuals run in barefoot and shod conditions with stride lengths that were both greater and less than their preferred shod stride length. They found the reduction in joint moments and GRFs was a function of stride length rather than shoe condition.20 The decreased sagittal plane joint moments can be explained by a decrease in the moment arm relative to the resultant GRF, a reduction in the magnitude of the GRF, or both. Decreasing stride length results in the foot being located more directly under the body at initial contact and leads to reductions in hip and knee flexion,17 factors that reduce moment arms relative to GRF.4

Confounding factors

1running-iStock_000017285887Large-copyWhile there is evidence to suggest that reducing stride length leads to biomechanical changes associated with reduced risk of running-related injury, there are several confounding factors that should be considered. First, decreasing stride length—particularly if it is achieved by switching from shod to barefoot running—may result in individuals contacting the ground initially with the forefoot rather than the rearfoot. In terms of injury risk, rearfoot ground contact requires tibialis anterior activation to decelerate plantar flexion as the foot is lowered to the ground. Correspondingly, rearfoot ground contact has been associated with increased pressures in the anterior compartment of the lower leg.33 Alternatively, when runners contact the ground with the forefoot, the triceps surae muscles activate to slow dorsiflexion, which has been associated with higher Achilles tendon strain and plantar flexor moments.34 Therefore, if reducing stride length is accompanied by a switch from a rearfoot-strike pattern to a forefoot strike pattern, the reduced risk of some running-related injuries could also mean an increased risk of other types of injuries.

Second, running velocity is the product of stride length and stride frequency. Therefore, stride frequency must be increased to maintain a given running velocity when stride length is reduced. Although decreasing stride length may reduce acute loading, increas-ing stride frequency means a greater total number of ground contacts. It is possible that lower loads applied more frequently may also increase injury risk. In terms of tibial stress fracture, Edwards et al reported that strain magnitude plays a more important role than the total number of loading cycles in stress fracture development.13 Additionally, Willson et al found that patellofemoral joint stress was lower with decreased stride length and, despite more strides per mile, patellofemoral joint stress per mile was also reduced.35 However, other musculoskeletal injuries may be more sensitive to the number of loading cycles.

Injury implications

While there is fairly extensive biomechanical research that supports the argument for runners adopting a shorter stride length, there is limited clinical research showing that gait retraining to attain shorter stride length is a successful modality to treat or prevent running-induced musculoskeletal injuries.

The earliest studies looking at the effect of stride length on musculoskeletal injury examined the effects of training male and female military recruits together. Jones et al found short female recruits had the greatest risk for running- and exercise-related injury and recommended that short women march at the front of columns to reduce their need to overstrike to keep pace with their taller colleagues.36 Additionally, Hill et al and Oxburn and Nichols found an increase in the number of pelvic stress fractures in female recruits that were attributed to the combined training of male and female recruits, which forced women to increase their stride length while marching.37,38 As a result of Hill et al’s research, the stride length for the Army Training Regiment was reduced to from 30 to 27 inches and researchers noted a resulting decrease in pubic ramus stress fractures.37

More recent studies have shown that gait retraining with reduction of stride length can be both a treatment modality and a means to reduce the risk of certain running-related musculoskeletal injuries. Given that the knee is the most frequent site of running-related musculoskeletal injury, several studies have examined the effect of reduction in stride length on clinical conditions surrounding the knee. Lenhart et al and Willson el al, respectively, examined the effect of decreased stride length during running on patellofemoral joint forces and joint stresses.35,39 Both groups found that decreasing stride length greatly reduced patellofemoral loading. Thus, it was suggested that decreasing stride length when running might be an effective means to change biomechanical factors that can contribute to patellofemoral pain.39 Additionally, Allen et al examined the effect of gait retraining with step rate manipulation as a treatment for ilio­tibial band syndrome.40 In this study, the authors found that a 5% increase in step-rate (resulting in decreased stride length) was an effective treatment for a single runner with iliotibial band syndrome when combined with a home exercise program that included stretching and strengthening.40

There is also evidence suggesting that decreasing stride length may help reduce the risk of stress fractures and muscle soreness in runners. Edwards et al used a finite element model to examine the effect of a reduction in stride-length on the probability of tibial stress fractures.13 The authors found that reducing stride length by 10% decreased the probability of stress fracture by up to 6%.13 Lastly, Rowlands et al examined the effect of stride-length manipulation on strength retention and muscle soreness with repeated bouts of downhill running.41 They found reducing stride length during downhill running decreased exercise-induced muscle damage and provided protection against muscle soreness.41

Indirect evidence

While not examining the effect of stride length directly, much of the research looking at the effect of barefoot running and minimalist shoes indirectly evaluates stride length, as barefoot/minimalist runners tend to adopt a reduced stride length. Clinical studies suggest that barefoot/minimalist running, and the resulting decreased stride length, may help reduce the risk of tibial stress fractures, patello­femoral pain, and plantar fasciitis.42 Further, forefoot-strike running, which is also associated with decreased stride length, has been shown to improve chronic exertional compartment syndrome.33 However, despite the reduction in stride length, barefoot/minimalist running may also lead to injury.43

1running-iStock_000032135952Medium-copyBarefoot/minimalist running has been associated with meta­tarsal stress fractures,44,45 and the transition to minimalist running has been associated with the development of foot bone marrow edema, a marker of added stress to the foot.45 It is possible that these injuries are due to a lack of cushioning under the foot. Additionally, forefoot ground contact, which is associated with decreased stride length and barefoot/minimalist running, has also been associated with higher Achilles tendon strain34 and increased risk of Achilles tendinopathy.46,47

Evaluating the literature on barefoot and minimalist shoe running can be difficult, as running in minimalist shoes is often thought to mimic barefoot running, but has in fact been found to have biomechanical characteristics more similar to shod running. Several studies have shown significant differences between barefoot running and running in minimalist shoes. Bonacci et al examined joint kinematic and kinetic variables in runners in barefoot and three shod conditions (minimalist shoe, racing flat, and regular athletic shoe).48 Their results showed significant differences between barefoot and shod conditions for kinematic and kinetic variables at the knee and ankle, but no significant differences between the three shod conditions.48 Further, McCallion et al compared several spatio­temporal variable of athletes running barefoot, in minimalist shoes, and in conventional running shoes.49 They found stride duration, flight time, and contact time were greater in conventional running shoes and minimalist shoes compared with barefoot running.49

Conclusion

In conclusion, decreasing stride length has been proposed as a method to treat and prevent running-related musculoskeletal injuries. While not directly examining the effect of stride length, research examining the effect of barefoot running and minimalist shoes indirectly evaluates stride length, as barefoot/minimalist runners tend to adopt a reduced stride length. Evidence suggests that decreasing stride length results in biomechanical changes, including reduced GRFs and joint moments, that can contribute to reduced injury risk. Clinical studies indicate that reducing stride length may help decrease the likelihood of stress fractures, iliotibial band syndrome, and patellofemoral pain.

Further research, including long-term prospective studies aimed at determining the effectiveness of decreasing stride length for successful treatment for specific musculoskeletal conditions, is needed. Additionally, studies examining running injury risk in barefoot/minimalist shoe conditions, and the resulting decrease in stride length, are needed to determine if shoe gear changes and the resulting gait changes are a successful means of reducing running-related injury risk, or if they could potentially lead to increased risk of certain injuries due to lack of forefoot cushioning.

Melissa Thompon, PhD, is an assistant professor of exercise science at Fort Lewis College in Durango, CO. Kristine Hoffman, DPM, is a podiatrist in private practice with Boulder Valley Foot and Ankle Clinic in Colorado.

Disclosure: The authors report that there are no conflicts of interest associated with this manuscript.

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