Hill tension intervals are a useful training method I implement with endurance athletes to help recruit more fast and forceful muscle fibers. Essentially, this improves neuromuscular capabilities, enhances running economy, and increases recruitment of fast muscle fibers late in a race when fatigue accumulates.
After a thorough warm up,
One to three sets of 10 x 20–40-second sprints up an 8 to 10% grade, with 2–4 minute recovery walk or easy jog down between each repeat, and a 5-7 minute easy flat ground jog recovery between sets.
All humans are made up of fast and slow twitch muscle fibers, with the arrangement and ratio of fast and slow twitch muscle fibers varying in humans based on genetics and training type. Sure, some humans are predisposed to having more of one set of fibers over the other, but that doesn’t mean we can’t train our muscles to be more “fast” or “slow.”
Depending on the sport for which we train, our muscles create different amounts of force under various lengthening or shortening velocities. The force–velocity relationship essentially states that the greater amount of force created, the less velocity is produced. Alternatively, higher velocity contractions or changes in muscle length limit the amount of force that can be produced.
For example, a one-repetition maximum deadlift requires a large amount of force to move the weight. Visually, you can see the weight is moving very slowly to the top of the lift. This is an example of a large-force/low-velocity muscle movement. Conversely, on the opposite end of the force–velocity curve, a squat jump is typically a body-weight or lower-weight exercise where you create enough force to move the weight in a very short duration, high-velocity muscle movement.
Why Is This Important for Endurance Athletes?
Endurance athletes typically have a higher ratio of slow twitch muscle fibers due to the metabolic demands of the sport. Slow twitch muscle fibers work with the body’s oxidative energy system, meaning oxygen is required to create energy, which allows us to do large volumes of training all at once. In contrast, if we were to do an all-out 10-second sprint, our body would be touching in on the immediate energy system and utilizing fast twitch fibers. Because this energy system is without oxygen, those immediate stores need a longer time to recover.
The order of muscle recruitment for any athlete, regardless of athlete type, is slow to fast. So, endurance athletes rarely utilize large forceful motor units because the training type is typically sub-maximal. However, training for larger force recruitment helps create more energy return with each foot strike, increasing the efficiency of sub-maximal running.
Additionally, maximizing muscle fiber recruitment helps the body maintain form late in a race. As we fatigue, we start to utilize anaerobic (non-oxidative) energy pathways to maintain above-threshold intensity. Fast twitch fibers are recruited at the onset of fatigue and are necessary for endurance performance.
Muscle tension intervals of 20–40-second uphill sprints.
These intervals maximize force production under a low-velocity muscle contraction. You often see cyclists implement this type of training in low rpm, big gear intervals, where the cyclist pushes big gears at rpms ranging from 45 to 60. As runners, we can mimic this type of training by performing steep, maximum hill sprints of 8–10% grade for 20 to 40 seconds.
In a study analyzing elite trained runners, researchers wanted to see the differences of six different hill repeat lengths. Lengths ranged from multiple 8–12-second sprints up to 2 x 25 minutes of sub-threshold running. Researchers concluded the greatest improvement in peak force, percent at VO2 max, and stride rate in the 8–12-second group. The group that completed 20–45-second steep gradient sprints, however, showed improvements in VO2 max, VO2 sub-max, lactate threshold velocity, velocity at VO2 max, and stride rate — all of which are critical for distance running performance.
These sprints help recruit large and fast muscle fibers over the entirety of the immediate and the glycolytic (anaerobic) energy systems, which creates large amounts of force under a low-velocity contraction. “Sprinting” and “slow” may seem contradictory, but this allows us to recruit large and forceful muscle fibers because the velocity of the muscle contractions is kept low by the length and grade of the hill. This training method also prevents muscle soreness with the low velocity muscle-movement, allowing for shorter recovery time.
When to Apply?
Muscle-tension intervals such as these are great to implement at the end of a large base build that includes frequent strides throughout the build, so connective tissue is strong and durable. Because they stimulate large muscle force recruitment throughout the entirety of anaerobic systems, with little muscle soreness, regular volume can be maintained. This allows for a greater transition into neuromuscular work and fast-turnover training because the foundations of high force abilities have already been established.
It is important to take into consideration your current fitness and training level. Beginners should start with one to two rounds whereas highly trained athletes can start with two, building to three rounds of 10 x 20-seconds with 2–4-minute rest recovery between each repeat. Eventually, as fitness builds over time, athletes can complete up to three rounds of 40-second intervals.
This workout is great to implement once a week, as your first intensity session of the week. This allows the muscles and central nervous system to be fresh to maximize adaptations. The intensity of the repeats should first focus on strong form and technique with your head up, arms parallel (think hip to nip), and strong hip and knee flexion and extension. You want to be able to build to an all-out sprint to maximize adaptations, but technique should never be lost in the process.
Additionally, one could pair this training method with high force-production strength training if your training status is high. Due to the high force adaptations, increases in neuromuscular capabilities, and increased running economy, you’ll transition quickly and easily into specific race training.
Lukus Klawitter is a Ph.D student at North Dakota State University with a research emphasis in sport physiology and biomechanics for endurance athletes. A coach with Matt Hanson Racing, he works with endurance athletes from all around the world. He has 6 years of cross-country and track and field coaching experience as well as coaching and research experience at altitude.