In-shoe plantar tri-axial stress profiles during maximum-effort cutting maneuvers

Abstract

Soft tissue injuries, such as anterior cruciate ligament rupture, ankle sprain and foot skin problems, frequently occur during cutting maneuvers. These injuries are often regarded as associated with abnormal joint torque and interfacial friction caused by excessive external and in-shoe shear forces. This study simultaneously investigated the dynamic in-shoe localized plantar pressure and shear stress during lateral shuffling and 45° sidestep cutting maneuvers. Tri-axial force transducers were affixed at the first and second metatarsal heads, lateral forefoot, and heel regions in the midsole of a basketball shoe. Seventeen basketball players executed both cutting maneuvers with maximum efforts. Lateral shuffling cutting had a larger mediolateral braking force than 45° sidestep cutting. This large braking force was concentrated at the first metatarsal head, as indicated by its maximum medial shear stress (312.2±157.0 kPa). During propulsion phase, peak shear stress occurred at the second metatarsal head (271.3±124.3 kPa). Compared with lateral shuffling cutting, 45° sidestep cutting produced larger peak propulsion shear stress (463.0±272.6 kPa) but smaller peak braking shear stress (184.8±181.7 kPa), of which both were found at the first metatarsal head. During both cutting maneuvers, maximum medial and posterior shear stress occurred at the first metatarsal head, whereas maximum pressure occurred at the second metatarsal head. The first and second metatarsal heads sustained relatively high pressure and shear stress and were expected to be susceptible to plantar tissue discomfort or injury. Due to different stress distribution, distinct pressure and shear cushioning mechanisms in basketball footwear might be considered over different foot regions.

Introduction

Lateral shuffling and sidestep cutting are frequently involved in offensive and defensive techniques in basketball. Game analysis has revealed that basketball players spend 31% of their playing time executing cutting movements, of which 20% are regarded as high-intensity movements (McInnes et al., 1995). Cutting maneuvers typically involve a sudden deceleration of the body, followed by acceleration in a new direction of movement. This places large external and internal loads on the lower limbs. McClay et al. (1994) investigated the ground reaction forces involved in 11 typical basketball movements including running, jumping, and cutting. The cutting and shuffling generated larger horizontal ground reaction forces than the other tested movements. Excessive horizontal ground reaction forces place large joint torque or shear stress on the ligaments or other soft tissues of the lower limbs, and are thought to be the mechanical factors of non-contact anterior cruciate ligament tear and ankle sprain (McKay et al., 2001, Yu and Garrett, 2007).

Foot skin and soft tissue problems are also very common, but are often neglected in studies of sports activities (De Luca et al., 2012). It has been suggested that these foot problems are associated with large in-shoe localized stress (Lord and Hosein, 2000, Mailler-Savage and Adams, 2006). A systematic review showed that up to 39% of marathon runners and 25.3% of triathletes experienced foot blisters (Gosling et al., 2010, Mailler-Savage and Adams, 2006). Foot blisters may cause intense pain and negatively influence sport performance. If serious complications arise, blisters can cause infection and subsequent disability.

The combined application of pressure and shear stress on the skin has been suggested as the critical risk factors for soft tissue problems (Yavuz and Davis, 2010, Zhang and Roberts, 1993). Excessive pressure and shear stress may occlude blood circulation (Bennet et al., 1979, Dinsdale, 1974) and reduce the tolerance and repair capability of tissues. Tissue response depends on the direction and magnitude of mechanical stress. Goldstein and Sanders (1998) found that tissue breakdown was rare at a low shear load but occurred at an earlier stage with greater shear stress. The level of shear stress may be a critical factor in predicting foot complaints due to cutting maneuvers. Abnormally high magnitude and frequency of shear stress may cause discomfort, hyperkeratosis, calluses and blisters on the foot (MacKenzie, 1974, Spence and Shields, 1968, Sulzberger et al., 1966), which may further affect athletic performance. Therefore, in-shoe shear evaluation is necessary to provide important biomechanical insights into the potentially harmful effects of interfacial tissue loading, especially during strenuous cutting movements.

Most of the existing cutting research has been conducted on external ground reaction forces (Cloak et al., 2010, Cordova et al., 1998, Cowley et al., 2006, McClay et al., 1994, Mclean et al., 2004) or plantar pressure (Eils et al., 2004, Orendurff et al., 2008). However, the external ground reaction forces do not directly reflect the mechanical actions at the foot–shoe interface, and in-shoe plantar pressure alone is not sufficient to predict plantar tissue problems (Cong et al., 2011, Lavery et al., 2003, Veves et al., 1992). Therefore, this study aimed to provide simultaneous measurements of regional in-shoe plantar pressure and shear stress during two typical cutting maneuvers for characterizing the loading distributions and profiles of plantar soft tissues.