How important is foot posture? Think about this question… what are your thoughts? I guarantee that the majority sports physiotherapists would be aware of the impact of foot posture on the lower limb kinetic chain. Thus, you sports physiotherapists would be aware of the predisposition to many overuse injuries that poor foot posture will give your athletes. No arguments there (I hope).
This link between foot posture (read: over-pronation) and overuse conditions has been well established in the literature. These conditions include the commonly seen plantar fasciitis (Pohl et al, 2009), Achilles tendinopathy (Ryan et al, 2009), and patellofemoral pain syndrome (Powers et al, 1995). This has lead to the practice in the sports medicine world of attempting to strengthen the musculature responsible for restricting and/or controlling foot (over)pronation. This article discusses the thinking behind these clinical decisions and research regarding the optimal exercise choice.
WHAT INTRINSIC FOOT MUSCLES ARE THE MOST IMPORTANT?
Whilst the various intrinsic foot muscles, including the flexor digitorum brevis and interosseous muscles, contribute to arch support during gait (Mann and Inman, 1964) the abductor hallucis receives considerable attention. This is because EMG studies have shown that abductor hallucis contracts to support the medial longitudinal arch and control pronation during static stance (Headlee et al, 2008). Interestingly, navicular drop will increase when the abductor hallucis is fatigued. Therefore, it has been suggested that strengthening and thus improving the endurance of these intrinsic foot muscles in athletes may reduce over-pronation, and the subsequent pathologies. Sounds logical, doesn’t it?
WHAT EXERCISES BEST STRENGTHEN THESE INTRINSIC MUSCLES?
A recent EMG study evaluated the muscle activation of abductor hallucis during two exercises used commonly in clinical practice; Short Foot and Toe Curl Exercises, shown in the videos below if you are not familiar with them (Jung et al, 2011).
The study participants randomly performed the two exercises in seated and single-leg stance positions. The authors then assessed the EMG muscle activity of abductor hallucis (%MVC) and the medial longitudinal arch angle under all 4 test conditions.
The authors found that the short foot exercise in single leg stance produced the best results with 73.2%MVC and a reduction in the medial longitudinal arch angle (or raise in navicular height). This is compared to 17.5%MVC for Toe Curls in single-leg stance. Therefore, the authors recommend the short foot exercise performed in single-leg stance to elicit maximum abductor hallucis muscle activity. Unfortunately, EMG muscle activity in the other intrinsic foot musculature was not measured and cannot be commented on.
THE EXERCISES IN QUESTION
Short Foot Exercise
Toe Curl Exercise
TAKE HOME MESSAGES AND CLINICAL IMPLICATIONS
- Abductor Hallucis is important for preventing excessive navicular drop and subsequent over-pronation
- The ‘Short Foot’ exercise elicits greater Abductor Hallucis EMG activity when compared to ‘Toe Curl’ exercises
- The ‘Short Foot’ exercise produces a smaller medial longitudinal arch angle, which correlates to higher navicular position, when compared with the ‘Toe Curl’ exercise
- Single leg stance elicits higher EMG activity than seated posture when performing short foot exercise.
- The effect of strengthening these intrinsic foot muscles has solid theoretical applications however the efficacy of this for injury prevention or management has not been scientifically examined.
Headlee DL, Leonard JL, Hart JM, Ingersoll CD, & Hertel, J. (2008). Fatigue of the plantar intrinsic foot muscles increases navicular drop. Journal of Electromyography and Kinesiology, 18, 420-425.
Jung DY, Kim MH, Koh EK, Kwon OY, Cynn HS, Lee WH. (2011) A comparison in the muscle activity of the abductor hallucis and the medial longitudinal arch angle during toe curl and short foot exercises. Physical Therapy in Sport 12;30-35
Mann R & Inman VT. (1964). Phasic activity of intrinsic muscles of the foot. Journal of Bone and Joint Surgery (Am), 46, 469-481.
Pohl MB, Hamill J & Davis IS. (2009). Biomechanical and anatomic factors associated with a history of plantar fasciitis in female runners. Clinical Journal of Sport Medicine, 19, 372-376.
Powers CM, Maffucci R & Hampton S. (1995). Rearfoot posture in subjects with patellofemoral pain. Journal of Orthopaedic and Sports Physical Therapy, 22(4), 155-160.
Ryan M, Grau S, Krauss I, Maiwald C, Taunton J & Horstmann T. (2009). Kinematic analysis of runners with Achilles mid-portion tendinopathy. Foot & Ankle International, 30, 1190-1195.