Friday, June 10, 2016

Strength, Stiffness and Elasticity: Improving Running Efficiency via Strength Training


Performance in distance running is between 80-99% dependent on aerobic metabolism. There are three ways to improve endurance: either improve lactate threshold, increase VO2 max or improve Running Efficiency (RE) or some combination of all three. This post will focus on strength training as a means to improve RE and lower metabolic costs.

There have been many studies over the years that have shown improved RE from low rep, relatively heavy weight training. Typically, runners weight training on their own or getting innappropriate coaching advice will go too light and perform too many repetitions per set in an attempt to recreate additional endurance work and/or avoid unwanted weight gain. This approach is misguided: the goal of improved RE requires the athlete to get stronger to generate higehr forces more rapidly, thus strength training with lower reps and heavier weights that tap into Type IIa fibers are appropriate. Doing so will compliment the slow twitch/sports specific skill training. Additionally, because the volume is low and the intensity is high, strength adaptations are mainly neuromuscular and do not involve muscle growth (hypertrophy) or associated weight gain. 

It may be that the primary factor between world champion marathoners and middle of the pack athletes is the ability to sustain efficient running technique for the duration of the race. Efficient running technique is highly dependent on strength, "In endurance running the stance leg absorbs three to four times the runner's bodyweight on each landing. To keep that up for a long time, endurance runners must be able to recruit relatively large motor units with submaximal effort - in other words, long distance runners have to be strong." (Bosch, pg125, Strength Training and Coordination) The stronger the runner, the less energy is required to run. 

Optimum RE can be thought of as repeatedly executing high forces while performing the least amount of work possible. Think of  it this way: isometric actions (no changes in length of the muscle) produce the highest forces but do no actual mechanical work and thus have lower metabolic costs. (Fenn Effect, Fenn 1924) Muscle fibers that do change length whether eccentric or concentric produce less force and do more work at higher metabolic expense. Therefore, runners whose technique produces mainly force (isometric actions that make use of the elastic properties of the muscle/tendon unit) will be mechanically and metabolically more efficient than a runner whose technique requires more mechanical muscular work and expends more energy. Perhaps "hitting the wall" towards the end of a race is as much a function of  insufficient strength contributing to technical inefficiency as it is lack of adequate fueling. 

Another way to think of it is strength training performed correctly teaches the athlete how to "take the slack out of the system" so the body can make as much use as possible of elastic properties: "free force"  The stronger the muscle, the better the athlete can reduce slack, the less effort is required to produce the stiffness and springiness which are hallmarks of efficient running technique.

Distance runners who engage in appropriate strength training while continuing to train their events should expect to see improved performance, enhanced technical endurance with no weight gain. Hitting the weights consistently could mean faster times with less perceived effort and greater fuel efficiency.