At first glance, this study doesn't seem so surprising
Fifteen men performed a heavy resistance toe flexor strength training program for their feet and ankles with 90% of their maximal voluntary isometric contraction for 7 weeks (560 contractions). At the end of the 7 week program push-off strength in the feet and ankles had more than doubled, toe strength had increased 10-15% and jump distance had increased on average about 7%.(Goldmann et al., 2013)
On the face of it, it makes sense that performing high resistance training for your foot muscles would indeed be quite effective, if not a well established method of improving foot strength. That last part is where you would be wrong. It has not been a well established fact. In fact so few people considered it a possibility that almost no one has studied it.
To date, there have been few attempts to measure and strengthen foot muscles while looking at changes in function. More specifically there are even fewer studies which look at the ability to specifically strengthen toe-flexor muscles and we have been somewhat sceptical that it would make the slightest difference. Further, of those that have attempted to do this before, the results have been somewhat disappointing (Spink, Fotoohabadi and Menz, 2010; Houck et al., 2017) which makes this study even more compelling.
Previous studies had asked participants to exercise their muscles with loads and in positions that are not functional i.e. don't represent loads typical of those experienced when walking and in positions that don't represent how the joint is used during activities such as walking, running, jumping or sprinting.
This study adds enormously to the rapidly growing research surrounding the importance of foot muscle strength. All people involved with rehabilitation, including those interested in foot, knee, hip and back function need to get with the program and grow their knowledge base.
Goldmann, J. P. et al. (2013) ‘The potential of toe flexor muscles to enhance performance’, Journal of Sports Sciences, 31(4), pp. 424–433. doi: 10.1080/02640414.2012.736627.
Houck, J. et al. (2017) ‘Can Foot Exercises Alter Foot Posture, Strength, and Walking Foot Pressure Patterns in People with Severe Flat Foot?’, AOFAS Annual Meeting, pp. 1–2. doi: 10.1177/2473011417S000199.
Spink, M. J., Fotoohabadi, M. R. and Menz, H. B. (2010) ‘Foot and ankle strength assessment using hand-held dynamometry: Reliability and age-related differences’, Gerontology, 56(6), pp. 525–532. doi: 10.1159/000264655.