Running is a popular form of physical activity with global participation (1). For some, running serves as a recreational activity, and others participate as competitive athletes. Various health benefits result from running including a reduced risk of cardiovascular disease, and overall healthier lifestyle (2). Despite the health benefits from participation, running has a high injury incidence rate (3, 4). For example, 37%–63% of those who participate in running suffer from some form of running-related injury (RRI) annually (3, 4). Some RRIs persist and could have lasting outcomes that impact runners' ability to participate, their health, and quality of life (5).

Most RRIs result from overuse and repetitive loading on the lower body (6, 7). Running is repetitive and involves cyclical mechanical loading applied to the lower extremity. Overuse of the lower limb structures in combination with potential predisposing risk factors contribute to the likelihood of injury incidence (7). Behavioural differences between recreational and competitive runners (e.g., quantity, frequency, intensity) also contribute to an increased risk of an RRI (8–12). For instance, a recreational runner has been defined as someone who runs a minimum of 3 times per week and totals 16 kilometers of running during the week (11). Comparatively, competitive runners run more frequently, and accumulate more than 100 km within a week (8, 10). The difference in exposure between different types of runners may contribute to injury susceptibility.

Running biomechanics also influence injury risk and performance. For instance, high performance runners have a longer flight phase compared with recreational runners due to faster velocity, and larger propulsive force during terminal stance (13, 14). Moreover, a lower step rate increases the risk of bone stress injury in collegiate cross-country runners (15), which may differ between different types of runners. Furthermore, lower limb position at foot contact has been investigated for its influence on injury and performance (16). A more perpendicular shank relative to the ground and closer contacts to the body's center of mass allows for greater running economy by decreasing the braking force at ground contact (16–18). A higher braking force decreases running performance and also increases risk of RRI (16, 18).

Additionally, other factors such as lower limb stiffness, ground reaction forces (GRF), and propulsion forces differ between runners and contribute to RRI and performance indicators (e.g., running speed and efficiency) (16, 17). The summed action of the ankle, knee, and hip extensors [i.e., total support moment (TSM)] contribute to propulsion during running (19). Moreover, the ankle plantarflexors contribute the largest component of positive work compared with the knee and hip extensors (20). However, these findings were in controls at relatively slower speeds, and it is unclear how joint work distribution differs between groups running at more typical training paces. Deficiency in the ankle plantarflexor moment and reliance on the knee and hip extensors in recreational runners may contribute to performance deficits and slower self-selected speeds when participating in long distance running (20). Comparisons of recreational and competitive runners elucidates optimal biomechanical strategies for performance given the known differences in self-selected running speeds.

The purpose of this study was to compare running biomechanics that have previously been linked to RRI and performance between recreational and collegiate runners. We hypothesized that collegiate runners would have more perpendicular shank angles and larger GRFs than their recreational counterparts. We also hypothesized that all lower extremity extensor moments would be higher in the collegiate group with the proportion of ankle moment as a percent of the TSM also higher in the collegiate group. A secondary purpose was to evaluate the association between GRFs and shank angle during running in recreational and collegiate runners. We hypothesized that a larger shank angle would be associated with a larger braking force in both groups.

Data used for this study were collected as part a larger study examining the association between running kinetics and femoral cartilage characteristics (21). All methods were approved by the university's institutional review board and participants provided informed written consent, before a single data collection session that lasted approximately 2-hours.

Descriptive statistics of participants demographic information can be found in Table 1. The recreational runners were older than the collegiate runners. The collegiate group reported greater amount of running and ran at a greater self-selected running speed compared with the recreational group. The collegiate group also had a greater proportion of midfoot and smaller proportion of rearfoot strike runners compared with the recreational group.

The primary purpose of this study was to compare injury- and performance- related running mechanics between recreational and collegiate runners. We further examined the association between ground contact and GRF characteristics within each group. The main findings indicated that collegiate runners used a larger proportion of the ankle extensors, but smaller proportion of the knee extensors compared with recreational runners. Moreover, collegiate runners had larger propulsive features (e.g., anterior force, vertical impulse) compared with recreational runners, and a more vertically oriented shank at ground contact (Figure 5). A more vertically oriented shank was associated with a larger propulsive impulse and smaller braking impulse.

We hypothesized that the joint moment distribution would differ between collegiate and recreational runners. Adjusting for speed, we found that the collegiate runners used a larger proportion of ankle extensor moment compared with recreational runners. The ankle plantar flexors are a large contributor to propulsion during running, and comprise the largest proportion of lower extremity joint work compared with the knee or hip extensors (20). Moreover, there is a distal to proximal shift in joint work during gait as speed increases from walking to sprinting (20, 29). As such, these findings suggest that collegiate runners use a more efficient strategy when speed is controlled that uses the ankle plantar flexors for propulsion. Moreover, the ability to utilize a larger proportion of the ankle plantar flexors when adjusting for speed likely increases their maximal running speed capacity relative to recreational runners and allow them to run at faster sub-maximal speeds for longer durations. Ankle power generation increases with faster running speeds and contributes to propulsion in recreational runners (14). Therefore, improving ankle plantar flexor function to reduce reliance on the hip and knee extensors during running may be a strategy to improve running performance in recreational runners and achieve similar self-selected speeds as collegiate runners during prolonged running.

The recreational runners had a larger knee extensor moment expressed as a percentage of TSM compared with collegiate runners when comparisons were adjusted for speed. A larger internal knee extensor moment contributes to greater patellofemoral contact stress (30, 31). As such, recreational runners utilize a running strategy that contributes to a disproportionate load on the patellofemoral joint that elevates risk for anterior knee pain (30, 32). Recreational runners may reduce their risk of injury from increasing the proportion of contribution from the ankle and hip joint extensor moments to the TSM. This contributes to reductions in knee extensor moment needed during running and decrease load to the patellofemoral joint. Conversely, collegiate runners may experience foot/ankle pathologies due to additional reliance on the ankle plantar flexors (33–35).

The collegiate runners in our sample had higher extensor moments but similar distribution of moments at every joint compared with recreational runners when comparisons were unadjusted for speed. These findings were expected and likely contributed to the overall difference in anterior force and self-selected running speed. Collegiate runners may have greater muscle capacity for joint extension from completing a larger training volume or supplementary resistance training (12, 36). These findings were supported by GRF comparisons, and collegiate runners who had greater propulsive force, and positive impulse compared with recreational runners. Supplementary forms of strength training with endurance training improves running economy, power, reactive strength, and running performance in collegiate runners (36). Therefore, improvements in running performance could be achieved in recreational runners by participating in supplementary resistance training similar to collegiate runners. Supplementary training may increase their muscle capacity at all joints for propulsive forces and positive impulse to the values that we observed in the collegiate group. Future research may aim to investigate if the additional of strength training to recreational runners could improve running speed.

We also found that recreational runners had higher vertical loading rates compared with collegiate runners when normalized to body weight. The vertical loading rate has been retrospectively (37), and prospectively (38), linked to tibial stress fracture (39, 40). However, these studies have largely been limited to recreational runners. In conjunction with our data, recreational runners may be at greater risk for stress fracture from elevated vertical loading rates. The vertical loading rate is strongly influenced by speed and foot strike pattern (41). As running speed increases, the vertical loading rate increases (41). Faster running speed also contribute to shift from rearfoot to a more anterior foot strike pattern for some runners (41). A more anterior foot strike pattern has been associated with reduced vertical loading rate compared with rearfoot contact at the same running speed (41). Collegiate runners in our sample ran faster and had a lower proportion of rearfoot strike runners. As such, faster speed and higher loading rates may have been mitigated by running with a more forefoot pattern (41). Collectively, these data suggest that collegiate and recreational runners have different biomechanics that contribute to unique injury patterns, and prospective data are needed to evaluate these hypotheses.

We also examined the association between shank kinematics at ground contact and GRF characteristics and found that a more vertically oriented shank was associated with less negative impulse and more positive impulse. The braking/posterior force has been prospectively linked to running-related injury (42), and a positive impulse is linked to faster running speeds (43). A prospective study on female recreational runners found that injury incidence was 8 times higher for runners with peak braking forces 0.27× body weight compared with 0.23× body weight (42). Moreover, a retrospective study found limbs with previous tibial stress fractures to demonstrate greater peak braking force values (44). Bone is stronger under compressive forces rather than shear force (45). Increased braking force could contribute to shear forces and greater bone-stress injury risk (44, 46). Furthermore, faster runners can apply 1.26 times greater average force per body weight in less time on the ground compared with slower runners, achieving 1.8 times faster top speeds (43). Elite runners have greater vertical forces 0.16 BW higher, and more vertical shank angle at ground contact compared with sub-elite runners (17). Therefore, our findings suggest that manipulating shank position presents a viable target for gait modification that may influence both injury risk and running performance. A more vertical shank angle at ground contact has been associated with better running performance and minimizes horizontal braking, which has been associated with better running economy and performance in distance runners (16). Furthermore, between laps one and two of an 800 m, the faster of the two laps presented a more vertical shank angle at ground contact in female distance runners at the world athletics championships (47). Our findings of a more vertically oriented shank in the collegiate group compared with recreational therefore, could be a biomechanical contributor to their faster running speeds. However, we note that our sample included some collegiate runners whose shank angles were slightly negative (i.e., leaned forward) rather than perpendicular, which may not be ideal. Moreover, correlation coefficients were only fair, and left a large portion of unexplained variance in GRF characteristics. Therefore, future studies should evaluate optimal shank angle during ground contact for both performance and injury prevention purposes.

Results of this study should be interpreted in the context of its limitations. Firstly, the cross-sectional study design negates the ability to evaluate if running mechanics are a result of different training magnitudes and behaviours of recreational and collegiate runners. Nonetheless, we still identified differences in running biomechanics that may contribute to the difference in ability of recreational and collegiate runners. Prospective data are needed to evaluate if running patterns change as a result of habitual training and can be manipulated via interventions (e.g., supplemental resistance training, biofeedback etc.). Secondly, we only examined self-selected running speeds to approximate habitual running. Our comparisons that statistically adjusted for running speed found differences in ankle and knee extensor contributions to the TSM that may influence propulsion. However, comparisons at matched speeds may further elucidate unique locomotive strategies that differentiate collegiate and recreational runners.

Collegiate runners compared with recreational runners demonstrated greater propulsion and a more vertically oriented shank that was associated with higher propulsive impulse and lower braking impulse. As such, runners could reduce braking forces that have previously shown association to tibial stress fractures by running with a more vertically oriented shank angle (42, 44, 46). A more vertical shank could also contribute to faster running through greater propulsion and less braking. Therefore, future studies may investigate the influence of altering shank angles on running performance and injury risk. Collegiate runners also used a greater proportion of the ankle extensors and smaller proportion of knee extensors than recreational runners when adjusted for speed. A greater contribution from the ankle joint compared with knee and hip at slower speeds may provide a more efficient propulsion strategy that allows for a larger capacity to increase running speed. Therefore, recreational runners may be able to achieve faster running speeds through greater proportional use of their ankle plantar flexors during propulsion.