If runners were superheroes, elastic recoil would be our superpower.
Elastic recoil occurs when you convert energy temporarily stored in tendons and fascia into a free push. Why free? Because it's fueled by the impact force of each foot strike. How big a push? The recoil generated by your Achilles tendons, plantar fascia and the fascia associated with your muscles provides up to 50 percent of the propulsive force for each stride. Best of all, it's trainable.
Tendons are the major driver of recoil. At rest, their tough collagen fibers line up in parallel wavy lines. Under tension, the wavy patterns straighten, allowing a stretch of 4 to 6 percent. The stiffer your tendons, the more energy it takes to stretch them. This energy is momentarily stored in your tendons, then released when your muscles contract.
When the impact force from each foot strike stretches your Achilles tendon, it is stored as energy. As your calf muscle reaches its maximum safe stretch, your stretch reflex causes your calves to contract. Simultaneously, your Achilles tendon (along with your plantar fascia and other fascia) releases its stored energy, creating a catapult effect--elastic recoil--that adds to the force generated by your muscles. And the faster the release of that recoil force (i.e., the shorter your ground contact time), the stronger the effect.
To appreciate recoil, try a simple exercise. Put your hand on your thigh and then tap your index finger as hard as you can. Next, pull back that index finger to its maximum safe stretch and then release it. Did it thwack your thigh a little harder than muscle-generated tapping alone?
To improve recoil, you need to increase the energy it takes to stretch your tendons by strengthening the fibers that make up tendons. Keep in mind that stretching a tendon beyond 4 to 6 percent is dangerous; more than 8 percent risks rupture. You'll also want to practice quick foot strikes to decrease ground contact time. After training your elastic recoil, you'll feel like you're running on coiled springs.
RESISTANCE TRAINING: Air squats and heel dips can be added to your post-run stretching and exercise routine to increase your recoil.
1. Air squats
Stand straight with your feet hip-width apart, toes pointed slightly out. Bend your knees, pushing your hips back until your thighs are parallel to the floor. Simultaneously swing your arms forward to shoulder height as a counterbalance. Repeat 10–15 times.
2. Heel dips
Balance on a platform or step using the balls of your feet, with your heels extending over the edge. Put all your weight on one foot and slowly lower that heel to its full range of motion. Use both feet to rise back up. Start with two to five reps; build to 15–20.
TECHNIQUE DRILLS & PLYOMETRICS: Always warm up well before drills and plyometrics. Take one to three minutes rest between sets.
3. High skipping
Skip forward while driving vertically off your toes and lifting the opposite knee high. Land on your takeoff foot, step forward and repeat with the opposite foot. Repeat for 20–60 meters, up to three sets.
4. Box jumps
Stand in front of a box at least a foot high. Jump onto the platform with both feet. Land and immediately jump backward to your start position, then spring back onto the platform again. Do five to 10 reps, up to three sets.
Spring from one foot to the other, driving off your toes and launching forward at about a 20- to 30-degree angle in front of vertical. Land on your opposite foot and bound again. Bound for 20–60 meters, up to three times.
6. Hill Sprints
Find a short, steep hill (start with 6 percent grade and work up to 10 percent) and sprint up it. Sprints should last 8 to 12 seconds. Do six to 10 reps with 1 to 3 minutes recovery between reps.
Pete Magill is the oldest American to break 15 minutes for 5K, with a 14:45 at age 49, and is co-author of the newly released book, Build Your Running Body