Sunday, January 17, 2010 | Category:
Training
99 percent of endurance runners utilize either a rear-foot-strike (RFS) or mid-foot-strike (MFS) pattern of contacting the ground during running (1). Research has shown that RFS and MFS produce different ground-reaction forces (GRF), both from the standpoints of maximum GRF and the rate at which peak GRF develops (2). The magnitude of GRF and the rate at which peak GRF is produced are likely to have significant impacts on the probability of running injury, and thus it is probable that RFS and MFS produce running injuries at different rates (3). Unfortunately, the specific effects of RFS and MFS on the frequency of overuse injury in running are currently very poorly understood.
The choice of RFS or MFS is also likely to have an impact on competitive performance and running economy. The fastest endurance runners in the world prefer MFS over RFS (4), and the most-economical endurance runners also favor MFS (5). Nonetheless, 75 to 85 percent of endurance runners employ RFS rather than MFS, and it is unclear whether a shift from RFS to MFS would be advantageous for these runners from performance and economy perspectives.
Relative Frequency of Different Foot-Strike Patterns
As mentioned, the two most commonly used foot-strike techniques for endurance running are the rear-foot strike (RFS), in which the heel of the running shoe is the first structure which makes impact with the ground during gait, and the mid-foot strike (MFS), in which the middle portion of the running-shoe sole makes initial contact (1). In a recent, elite-level half-marathon, about 75 percent of participants were using the RFS pattern at the 15-K point of the race, with 24 percent utilizing MFS and 1 percent engaged in fore-foot strike (FFS) (ibid). Many exercise scientists and coaches recommend the more-popular RFS pattern as the optimal ground-contact strategy, probably because a well-accepted belief in the running community is that RFS leads to lower overall impact forces, compared with MFS (6).
Although experienced runners tend to favor RFS over MFS by at least a three-to-one margin (7), motion analysis of Olympic-Games competitors has suggested that Olympic medalists avoid RFS and utilize MFS exclusively (8). Video analysis of world-champion and world-record-holding runners, including Paul Tergat, Haile Gebrselassie, and Paula Radcliffe, has indicated that such competitors employ MFS and occasionally fore-foot strike (FFS), not RFS, both while training and competing (4). Research has convincingly shown that the frequency of MFS increases with competitive ability; in one study carried out with elite-level runners, 36 percent of the male, top-50 finishers employed MFS in a competition, vs. just 20 percent of the 51st to 200th-place runners in the same race (1). In this investigation, MFS was utilized by three of the first seven female finishers (43 percent) but by only four of the other 28, slower women in the race (14 percent).
Potential Effects of Foot-Strike-Pattern Technique on Performance
Compared with RFS, performance may be enhanced with MFS because average ground-contact time is shorter (by 17 milliseconds at a running velocity of approximately 5 to 5.5 meters per second and by approximately 10 milliseconds at slower speeds) (1 & 9). As a consequence of the more-abridged contact time, stride rate is also higher for MFS (ibid). Improvements (decreases) in ground-contact time and increases in stride rate have been linked with enhanced running economy and faster 5-K performances (10). In addition, a key difference between the top competitors in an elite road race and the slower elite performers in the same competition is the shorter average ground-contact time of the faster finishers (1). Such findings suggest that MFS may be the superior foot-strike pattern from a competitive standpoint.
Effects of Foot-Strike Pattern on Running Economy
Research has revealed that runners tend to adopt the most-economical running style possible for their individual anatomical and physiological characteristics (11). At least 75 percent of experienced runners favor RFS over MFS, suggesting that rear-foot striking may be the most-economical pattern. In addition, a peer-reviewed study detected enhanced economy with RFS, compared with MFS (12). However, this investigation was carried out with relatively inexperienced runners who may have had little time to perfect the MFS technique.
Although RFS is more popular than MFS, it is important to bear in mind that the world’s-best endurance runners have undoubtedly optimized most aspects of their running mechanics and performance-relevant physiological characteristics, including running economy. Given that running economy is such a strong predictor of performance (13), the ubiquity of MFS among super-elite runners suggests that MFS may produce highly economical running.
Compared with RFS, it is also clear that MFS leads to a less-extended leg at foot strike and a shorter time of maximum knee flexion during the support phase of gait (14). This suggests that MFS produces a shorter period of muscle activation per running step, which might decrease the oxygen cost of running and lead to enhanced economy with the MFS pattern. Furthermore, the use of MFS increases the relative amount of eccentric work performed at the ankle during running (15). Since eccentric actions consume less oxygen, compared with concentric activities, for a given quantity of work, MFS should thus be associated with enhanced economy.
One of the investigators in this study (Dr. Anderson) has had extensive experience coaching, managing, and advising elite Kenyan runners, including such notables as Leah Malot (African 10-K champion) and Benjamin Simatei (winner of Park Forest 10-Mile Race). His personal work with internationally successful Kenyans has revealed that nearly every top Kenyan follows the MFS strategy. It is interesting to note that scientific inquiries have demonstrated superior economy in elite Kenyan endurance runners, compared with top-level athletes from other parts of the world (5 & 16)). This research suggests that MFS is associated with more-economical running, compared with RFS.
Impact of Foot-Strike Pattern on Muscle Damage and Overuse Injury
Ground-reaction force (GRF) is thought to be an important predictor of running injury (17, 18, & 19); runners with higher vertical maximal forces tend to experience greater lower-extremity pain, and elite runners with elevated ground-reaction forces tend to have an increased risk of stress fracture (20). The extent of motion around the ankle and knee joints during gait is also believed to be a predictive factor for injury (21).
It is clear that MFS and RFS produce different patterns of ground-reaction force (22). Runners who employ RFS generally demonstrate a pronounced, initial spike in vertical GRF during the first few moments of stance which is usually absent when MFS is the ground-contact strategy; this transient upswing in GRF with RFS is thought to be a significant cause of injury (23). In contrast, average peak-to-peak amplitude for medio-lateral GRF can often be three times greater in MFS runners, compared with RFS competitors (24). Such medio-lateral forces are of considerably lower magnitude, compared with vertical forces, however, often cresting at just 10 percent of vertical GRF.
Research reveals that MFS and RFS are associated with different patterns of muscular work, force production and power absorption in various parts of the leg during running. Compared with RFS, MFS has been linked with higher peak power absorption and eccentric work at the ankle during gait (15). It is possible that these effects may lead to an overworking of the lower-leg muscle groups and increase the risk of Achilles-tendon injury for MFS runners (1). Other research has suggested that runners who attempt to “convert” from RFS to MFS experience significant muscle fatigue and severe delayed-onset muscle soreness (??) (although these factors may merely be the result of a change in running style and thus motor-recruitment patterns, rather than a reflection of the negative characteristics of MFS).
Although RFS may reduce the forces placed on the ankle during running, research suggests that it tends to increase the power absorption and total work performed at the knee, compared with MFS (15). Thus, it is possible that RFS could be connected with a higher rate of knee injury, compared with MFS.
Scientific inquiry supports this possibility. Runners employing RFS tend to strike the ground initially with the lateral side of the heel, and research has indicated that RFS with lateral contact is linked with a higher risk of LLOI (25). Another investigation has revealed that runners exhibiting a high vertical peak force under the lateral portion of the heel during ground contact are at increased risk of patello-femoral injury (26).
Finally, accelerometers attached to the skin or embedded in the tibia have been utilized to gauge loads placed on the lower extremity during running. Accelerometer studies demonstrate that peak acceleration measures are greater at slower stride rates (and thus longer stride lengths) for any specific running speed (27). Such data suggest that the loading rate for impact forces would be lessened by a shift from RFS to MFS, since the latter is strongly linked with higher stride rates and shorter strides. Research suggests that loading rate is an important risk factor for LLOI.
Although research has produced somewhat-conflicting results in this area, the bulk of the available evidence suggests that MFS produces a more-favorable force-production pattern. Thus, MFS should be linked with a lower rate of injury.
No previous study has explored the connections between a change in foot-strike pattern from RFS to MFS and alterations in performance, running economy, and injury rate. The purpose of an upcoming study is to examine the consequences of a change in landing technique during running from RFS (the most-popular pattern) to MFS. It is hypothesized that this transformation will lead to more-abridged ground-contact times higher stride rates, and enhanced economy – and thus upgraded 5-K performances. It is further hypothesized that the transition to MFS will reduce muscle strain during long runs and high-volume training weeks, thus decreasing the likelihood of overuse injury.
References
(1) “Foot Strike Patterns of Runners at the 15-Km Point during an Elite-Level Half Marathon,” Journal of Strength and Conditioning Research, Vol. 21 (3), pp. 888-893, 2007
(2) “Ground Reaction Forces in Distance Running,” Journal of Biomechanics, Vol. 13, pp. 397-406, 1980
(3) “Biomechanics of Distance Running,” In Current Issues in Biomechanics, M. D. Grabiner, Ed., Champaign, Illinois: Human Kinetics, 1993, pp. 3-31
(4) Walt Reynolds, personal communication based on video analysis of world-record holders
(5) “Kenyan Dominance in Distance Running,” Comp Biochem Physiol A Mol Integr Physiol, Vol. 136 (1), pp. 161-170, 2003
(6) “Effects of a Verbal and Visual Feedback System on Running Technique, Perceived Exertion, and Running Economy in Female Novice Runners,” Medicine & Science in Sports & Exercise, Vol. 21 (2), p. S80, 1989
(7) “Foot Strike Patterns in Distance Running,” In Biomechanical Aspects of Sport Shoes and Playing Surfaces: Proceedings of the International Symposium on Biomechanical Aspects of Sports Shoes and Playing Surfaces, B. A. Kerr, Ed., Calgary, Alberta: University Press, 1983, pp. 135-142
(8) “The Motion Analysis of a Gold Medal Marathon Runner Naoko Takahashi during the Race at Sidney Olympic,” Monthly Journal of Track and Field, Vol. 8, pp. 146-151, 2002
(9) “Bioengineering Analysis of Muscle and Joint Forces Acting in the Human Leg during Running,” In B. Jonsson, Ed., Biomechanics X-B, Champaign, Illinois: Human Kinetics, pp. 855-861, 1987
(10) “Explosive-Strength Training Improves 5-Km Running Time by Improving Running Economy and Muscle Power,” Journal of Applied Physiology, Vol. 86, pp. 1527-1533, 1999
(11) “The Effect of Stride Length Variation on Oxygen Uptake during Distance Running,” Medicine & Science in Sports & Exercise, Vol. 14, pp. 30-35, 1982
(12) “Relationship between Distance Running Mechanics, Running Economy, and Performance,” Journal of Applied Physiology, Vol. 63, pp. 1236-1245, 1987
(13) “Running Economy: The Forgotten Factor in Elite Performance,” Sports Medicine, Vol. 37 (4-5), pp. 316-319, 2007
(14) “Lower Extremity Mechanics in Runners with a Converted Footstrike Pattern,” Journal of Applied Biomechanics, Vol. 16, pp. 210-218, 2000
(15) “Reduced Eccentric Loading of the Knee with the Pose Running Method,” Medicine & Science in Sports & Exercise, Vol. 36, pp. 272-277, 2004
(16) “Aerobic Exercise Capacity at Sea Level and at Altitude in Kenyan Boys, Junior and Senior Runners compared with Scandinavian Runners,” Scandinavian Journal of Medicine & Science in Sports, Vol. 5 (4), pp. 209-221, 1995
(17) “Biomechanics, Load Analysis, and Sports Injuries in the Lower Extremities,” Sports Medicine, Vol. 2, pp. 367-379, 1985
(18) “Injuries to Runners,” American Journal of Sports Medicine, Vol. 6, pp. 40-50, 1978
(19) “Running Symposium,” Foot and Ankle, Vol. 1, pp. 190-224, 1981
(20) “Biomechanical Effects of Pain and Sportshoe Corrections,” Australian Journal of Science and Medicine in Sport, Vol. 16 (1), pp. 10-16, 1984
(21) “Biomechanical Aspects of Distance Running Injuries,” in Biomechanics of Distance Running Injuries, P. R. Cavanagh, Ed., Champaign, Illinois: Human Kinetics, 1990, pp. 249-269
(22) “Biomechanics of the Foot during Locomotion,” in Current Issues in Biomechanics, M. D. Grabiner, Ed., Champaign, Illinois: Human Kinetics, 1993, pp. 33-52
(23) TBP
(24) TBP
(25) “A Prospective Study on Gait-Related Intrinsic Risk Factors for Lower Leg Overuse Injuries,” British Journal of Sports Medicine, Vol. 43 (13), pp. 1057-1061, 2009
(26) “Gait-Related Intrinsic Risk Factors for Patellofemoral Pain in Novice Recreational Runners,” British Journal of Sports Medicine, Vol. 42 (6), pp. 466-471, 2008
(27) “The Effect of Varied Stride Rate Upon Shank Deceleration in Running,” Journal of Sports Sciences, Vol. 3, pp. 41-49, 1985