Running Gait Assessment

Introduction

Musculoskeletal running-related injuries occur when there is an imbalance between tissue tolerance and applied loads experienced by the body. Reasons and risk factors for this imbalance are complex and multifaceted. However, a runner's mechanics significantly influence the extent of loading applied to the musculoskeletal system. This is evidenced by differences in the mechanics of runners with and without injuries or those with a history of injury. Moreover, there is growing evidence for the benefit of gait retraining (i.e., correcting mechanics that are thought to contribute to current injury through feedback and cueing) in resolving pain and risk factors associated with injury. Thus, observation of running mechanics is essential to the comprehensive evaluation and treatment of an injured runner.

Running biomechanics can be described using three broad categories: spatiotemporal measures, kinematics, and kinetics. Spatiotemporal measures are the basic characteristics of a runner's stride. These include stride length and frequency, step width, vertical center of mass (COM) displacement, flight time, and ground contact time. Spatiotemporal characteristics help to discern running from walking gait. For instance, step widths are shorter, stride frequencies are higher, and there is presence of a flight phase (denoted by flight time) when running. Running speed heavily influences spatiotemporal characteristics. Moreover, stride measures are interrelated, where a change in one parameter often results in subsequent changes in other parameters.

Kinematics describe body segment (e.g., thigh or shank) orientation during movement without regard to the forces that cause the movement. Kinematics are typically described with respect to the plane of movement and referenced as joint angles or body segment orientations. For instance, knee flexion/extension occurs in the sagittal plane, knee abduction/adduction in the frontal plane, and knee internal/external rotation in the transverse plane. Kinematics can also help to delineate walking from running gait. Typically, running results in a larger range of motion, particularly for lower limb joints, than walking. The larger range of motion demonstrated in running is a result of the increased muscular requirement needed to propel off the ground and land again without collapsing.

Kinetics refers to the cause of movement and reflects the power, forces, and energy associated with movement. Ground reaction force (GRF) is the force that reacts to the push transmitted to the ground by the foot of the runner and can be decomposed into three orthogonal components. These components are vertical, anteroposterior, and medial-lateral. With respect to running, the vertical component of GRF has received the most attention in the literature. The vertical GRF curve in running has one distinct peak. At contact, the vertical GRF spikes sharply to create an initial, or impact, peak. However, depending on foot strike pattern and running form, an impact peak may not always be present. The highest magnitude peak in running occurs at midstance and is described as the active peak because it roughly equates to the amount of muscle activity needed to support body weight against the pull of gravity. This accounts for approximately 80% of the metabolic cost of gait. The active peak depends on the mass and speed of the runner and can only be affected minimally without a significant increase in metabolic demand. The active peak in running is approximately 2.2–2.8 times the body weight in a typical distance runner compared with approximately 1.1 times body weight in walking. At higher speeds, when more muscle activity is needed for support, active peak values increase.

An understanding of the forces that drive motion (kinetics) as well as typical lower limb joint ranges (kinematics) can aide in the evaluation of the potential mechanisms of running-related injury. Some kinematic and kinetic characteristics have been identified as global indicators of injury. These global indicators are high vertical GRF loading rates and poor lower limb dynamic alignment, namely excessive hip adduction, internal rotation, and pelvic drop. For instance, higher vertical GRF loading rates have systematically been found in runners with leg and foot tendinopathies, tibial stress fractures, and other running-related bone stress injuries. Likewise, abnormal frontal and transverse plane movement patterns at the hip have been found in runners with tibial stress fractures, patellofemoral pain, and iliotibial band syndrome. These running kinematics and kinetics are often targeted in clinical gait retraining interventions, directly or indirectly, as a means to reduce pain and restore function in runners with knee and leg injuries. Additionally, these biomechanical measures are frequently screened to determine injury risk. Directly monitoring kinetics outside a laboratory setting is not feasible because this requires expensive instrumentation (e.g., force-sensing insoles, force platforms). However, recent studies have identified kinematic correlates , or two-dimensional running mechanics that can be captured in the clinic and that are associated with GRF measures.

A comprehensive evaluation of multiple factors is necessary when assessing runners with a repetitive stress injury. Critical components of the evaluation include (1) detailed subjective history and current training habits; (2) observation of structural alignment; (3) assessment of strength, flexibility, and their counterparts in functional testing—stability and mobility; and (4) gait analysis. A systematic approach to assessment is worthwhile to develop. This will expedite the testing to rule out contributing factors and will facilitate areas of potential impairment which may lead to dysfunction. Starting with structural observation, functional standing tests will elucidate potential problem areas that require further investigation. For instance, lack of full descent during a double-leg squat as a result of restriction in ankle range of motion signals that further examination of structural or neuromuscular components related to lack of tibial progression over the foot is warranted and should be performed in an unloaded position (e.g., during exam table testing). Clinical testing should end with assessment of running gait. This format allows for all information gleaned from history, functional screening, musculoskeletal examination, and postural observation to be fully integrated into the clinical diagnosis of contributing factors to running-related injury.

Subjective History

A detailed account of the individual's medical history, injury history (running-related or otherwise), training habits, and present condition is necessary to lay the foundation on which to build clinical hypotheses about contributing factors to current injury. It is paramount to gain information about all prior musculoskeletal injuries, regardless of whether they occurred as a result of running. Prior injuries often create areas of nonpainful dysfunction or compensatory patterns that may increase susceptibly to current injury. Useful information with regard to training habits includes weekly running volume, running schedule, average pace, running surface, type of running shoe (number of pairs, prescribed or self-selected), use of orthotics (custom or over-the-counter), cross- or supplementary (e.g., tissue mobility) training, recovery techniques (e.g., ice post-run), and previous training and race experience. It is also helpful to obtain information about the runner's goals for running (e.g., competitive, social, weight control) because this may influence current training habits.

Once history is complete, information on present symptoms must be obtained. It is paramount that clinicians ask about the onset, duration, locality, and intensity of symptoms with regard to running. For example, pain that is present at the start of a run and progressively lessens over the duration of a run may indicate a soft tissue or tendinous origin. In contrast, pain that is not present at running onset but builds over the course of a run or with increased training difficulty may signal insufficient neuromuscular activation that is exposed by fatigue or insufficient muscle strength.

Postural Observation

Current research has limited evidence indicating that structural alignment is a primary risk factor for injury. However, a runner's structure and alignment provide meaningful insight into the basic internal constraints influencing habitual movement patterns. Observation should be performed systematically—either starting at the head or feet—and with views of all three points of view (front, back, side). Runners should be barefoot and in as little clothing as their comfort level allows. For men, this may be spandex or running shorts where the knee and thighs are exposed to view quadriceps muscle mass. For women, a sports bra or tight-fitting tank top is appropriate along with spandex or running shorts. It is helpful to take postural pictures from all views for further examination and to illustrate current habitual patterns. Set up a spot in the clinic so that pictures are always taken at the same distance. The clinician should attend to both the local and global postural deviations. For example, identification of dropped shoulder position should be noted independently and considered with additional postural observations (elevated right hip, slight right rotation of the pelvis, head tilt, ankle pronation) to understand compensation along the entire kinetic chain. Standing alignment, spinal curvatures, muscle tone, right-to-left asymmetry, weight distribution (right to left, front to back), and skin appearance should be fully examined and documented. A plumb line or grid may be helpful in the background to do this.

The wear pattern of habitual running shoes is important to examine, particularly if shoes have accumulated mileage. Most runners have a rearfoot strike pattern and hit the ground on the posterolateral aspect of the heel, so wear to this area is not uncommon. However, other patterns may provide clinical clues. Excessive stretch on the medial aspect of the shoe fabric may indicate increased pronation during running, whereas fraying or holes along the medial aspect indicate crossover gait, a common feature of iliotibial band syndrome. Holes on the top of the shoe over the second metatarsus may signal restriction in posterior calf musculature and potential lower leg issues (anterior shin splints, Achilles tendinopathy). Excessive stretched heel counter or bilateral wear on the medial and lateral aspects of the heel may indicate foot instability at landing and typically correspond to lower leg issues (Achilles tendinopathy, retrocalcaneal bursitis, gastrocnemius strain, plantar fasciitis).

Functional Tests

The most common functional movements assessed in runners are single-leg squat, double-leg squat, step down, single-leg hop, and single-heel raise. Dynamic alignment, neuromuscular control, functional mobility, quality of movement, and right-to-left symmetry should be evaluated during each movement.

Single-Leg Squat

Running is essentially hopping from one leg to the other in a forward progression. The single-leg squat, or slight variations of this movement, has been the most extensively studied assessment tool used during athletic screening. It requires minimal to no equipment and provides immediate information about problematic areas in the athlete's movement patterns. Increased medial position of the knee over the planted foot (i.e., dynamic valgus) during a single-leg squat movement has been associated with common running-related injuries in adults. Although knee position receives the most attention, other aspects of the movement can elucidate deficits in postural stability, hip strength, core strength, and trunk control.

For the single-leg squat test, have the runner stand barefoot with hands on hips and eyes level. Take note of overall pattern and isolated segment issues. Have the runner descend to approximately 45 degrees to 60 degrees of knee flexion because this is typically peak joint angle during running. The runner should perform at least 10 consecutive single-leg squats at a relatively constant rate. Repeated squats will more readily elucidate any mechanical deviations as well as any neuromuscular deficiencies. Evaluate foot and ankle function because this cannot be seen during running due to footwear. Make note of toe clawing, arch displacement and height, foot stability, and weight distribution both in standing and during descent. Quality of movement, ease of movement, and patient apprehension should be noted in addition to positional deviations.

Double-Leg Squat

The double-leg squat allows for simultaneous assessment of sagittal plane mobility at multiple joints, trunk control, and triplanar foot mechanics. The runner should stand barefoot with feet slightly wider than hip width. Heels should be flat on the ground, and arms should be held in a Y-position overhead. Instruct the runner to squat as deeply as possible, keeping heels on the ground and arms in position. As with the single-leg squat test, the runner should perform repeated, successive squats at a fairly constant rate. Observe movement from the front, side, and back. Make note of right-to-left asymmetries as well as any primary limitations for achieving full range of motion during a squat. Key areas to observe are transverse and frontal plane motion at the foot and lumbo-pelvic-hip complex during descent. Runner feedback can help to determine primary restriction. For instance, descent into deep squat may be limited by apparent ankle joint range of motion. However, the runner may state that it is the restriction in the posterior calf that limits full squatting ability. Querying the runner about areas of discomfort or perceived restriction will facilitate a streamlined exam during the table assessment that immediately follows this functional testing.

Single-Leg Hop

The single-leg hop test is performed much like the single-leg squat test. The runner should be barefoot and hop several times on each leg using a constant rate. Control during landing, particularly at the trunk and knee, along with vertical height should be assessed during movement.

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