The big final step to the shuttle. It loads roughly 2.5 times your body weight — your knee stays over or behind your toes, never in front of them.
The lunge is the most expensive movement in badminton: peak forces of roughly 2.5 times body weight, with the Achilles tendon taking 6 to 12 times and the patellar tendon around 5 times your weight. No surprise that knee and ankle are where most injuries happen. What separates elite players from amateurs is less strength than the foot: amateurs land on the lateral forefoot and roll the ankle outward — the direct route to a sprain. Better players load the medial forefoot and shift heel to ball, with the knee and trunk actively stabilised. Don't turn your foot outward in a deep lunge; it measurably raises the load on the knee. What often goes unnoticed: the jump smash isn't the risk, the landing and the deep lunge on a twisted foot are — and indoor shoes with lateral support matter more here than any pricier racket.