It has been shown that mechanical energy is dissipated at the metatarsophalangeal (MTP) joint during running and jumping. Furthermore, increasing the longitudinal bending stiffness of the midsole significantly reduced the energy dissipated at the MTP joint and increased jump performance. It was hypothesized that increasing midsole longitudinal bending stiffness would also lead to improvements in running economy. This study investigated the influence of midsole longitudinal bending stiffness on running economy (performance variable) and evaluated the local effects on joint energetics and muscular activity. Carbon fiber plates were inserted into running shoe midsoles and running economy, joint energy, and electromyographic (EMG) data were collected on 13 subjects. Approximately a 1% metabolic energy savings was observed when subjects ran in a stiff midsole relative to the control midsole. Subjects with a greater body mass had a greater decrease in oxygen consumption rates in the stiff midsole relative to the control midsole condition. The stiffer midsoles showed no significant differences in energy absorption at the MTP joint compared with the control shoe. Finally, no significant changes were observed in muscular activation. Increasing midsole longitudinal bending stiffness led to improvements in running economy, yet the underlying mechanisms that can be attributed to this improvement are still not fully understood.

Objectives: To determine if measurements of static lower limb alignment are related to lower limb injury in recreational runners. Methods: Static lower limb alignment was prospectively measured in 87 recreational runners. They were observed for the following six months for any running related musculoskeletal injuries of the lower limb. Injuries were defined according to six types: R1, R2, and R3 injuries caused a reduction in running mileage for one day, two to seven days, or more than seven days respectively; S1, S2, and S3 injuries caused stoppage of running for one day, two to seven days, or more than seven days respectively. Results: At least one lower limb injury was suffered by 79% of the runners during the observation period. When the data for all runners were pooled, 95% confidence intervals calculated for the differences in the measurements of lower limb alignment between the injured and non-injured runners suggested that there were no differences. However, when only runners diagnosed with patellofemoral pain syndrome (n = 6) were compared with non-injured runners, differences were found in right ankle dorsiflexion (0.3 to 6.1), right knee genu varum (−0.9 to −0.3), and left forefoot varus (−0.5 to −0.4). Conclusions: In recreational runners, there is no evidence that static biomechanical alignment measurements of the lower limbs are related to lower limb injury except patellofemoral pain syndrome. However, the effect of static lower limb alignment may be injury specific.

Shoe inserts and orthotics for sport and physical activities. Med. Sci. Sports Exerc., Vol. 31, No. 7(Suppl.), pp. S421-S428, 1999. The purposes of this paper were to discuss the perceived benefits of inserts and orthotics for sport activities and to propose a new concept for inserts and orthotics. There is evidence that inserts or orthotics reduce or prevent movement-related injuries. However, there is limited knowledge about the specific functioning an orthotic or insert provides. The same orthotic or insert is often proposed for different problems. Changes in skeletal movement due to inserts or orthotics seem to be small and not systematic. Based on the results of a study using bone pins, one may question the idea that a major function of orthotics or inserts consists in aligning the skeleton. Impact cushioning with shoe inserts or orthotics is typically below 10%. Such small reductions might not be important for injury reduction. It has been suggested that changes in material properties might produce adjustments in the muscular response of the locomotor system. The foot has various sensors to detect input signals with subject specific thresholds. Subjects with similar sensitivity threshold levels seem to respond in their movement pattern in a similar way. Comfort is an important variable. From a biomechanical point of view, comfort may be related to fit, additional stabilizing muscle work, fatigue, and damping of soft tissue vibrations. Based on the presented evidence, the concept of minimizing muscle work is proposed when using orthotics or inserts. A force signal acts as an input variable on the shoe. The shoe sole acts as a first filter, the insert or orthotic as a second filter, the plantar surface of the foot as a third filter for the force input signal. The filtered information is transferred to the central nervous system that provides a subject specific dynamic response. The subject performs the movement for the task at hand. For a given movement task, the skeleton has a preferred path. If an intervention supports/counteracts the preferred movement path, muscle activity can/must be reduced/increased. Based on this concept, an optimal insert or orthotic would reduce muscle activity, feel comfortable, and should increase performance.

Background: Identification of mechanical factors associated with patellofemoral pain, the most prevalent running injury, is necessary to help in injury prevention, but unfortunately they remain elusive. Hypothesis: Runners who develop patellofemoral pain have increased knee joint angular impulse in the frontal plane. Study Design: Case control study; Level of evidence, 3. Methods: A retrospective study compared knee abduction impulses of 20 patellofemoral pain patients with those of 20 asymptomatic patients. A second prospective study quantified knee angular impulses during the stance phase of running of 80 runners at the beginning of the summer running season. Epidemiologic data were then collected, recording the type and severity of injury of these runners during a 6-month running period. Results: The patellofemoral pain patients in the retrospective study had significantly higher (P =. 026) knee abduction impulses (17.0 ± 8.5 Nms) than did the asymptomatic patients (12.5 ± 5.5 Nms). Six patients developed patellofemoral pain during the prospective study. The prospective data showed that patients who developed patellofemoral pain had significantly higher (P =. 042) knee abduction impulses (9.2 ± 3.7 Nms) than did matched patients who remained uninjured (4.7 ± 3.5 Nms). Conclusion: The data indicate that increased knee abduction impulses should be deemed risk factors that play a role in the development of patellofemoral pain in runners. Clinical Relevance: Footwear and running style can influence knee angular impulse, and the appropriate manipulation of these variables may play a preventive role for patients who are predisposed to patellofemoral pain.