Plyometrics: Free speed for endurance athletes

Most people can generally understand training specificity, run more, and I’ll get better at running. Simple, at least until you can’t go running as much as you’d like - maybe because you have a busy work week, family commitments or there’s a global pandemic. Then you must get more creative. One of the more under-utilized concepts of training specificity is training for the adaptations beneficial to the event, rather than just training the event itself. Essentially, if I want to get better at long-distance triathlon (LDT) performance, what metabolic, structural, and neural adaptations do I need to make me stronger, last longer, and ultimately perform better? While you don’t need to start squatting 400 lbs (in fact please don’t!), plyometric training falls into this specific strength category (i.e. hill running, big gear cycling, core training, posture, etc.), which can be valuable to target adaptations directly beneficial to endurance training. Traditionally, endurance athletes and coaches have focused on metabolic adaptations, while strength and conditioning coaches tend to focus more on neuromuscular adaptations, but the secret is out! They’re not mutually exclusive; endurance coaches may want to learn a bit from the foreign world that is strength and conditioning.

What is plyometric training?

Plyometric training is a uniquely viable method to enhance jumping, sprinting, and endurance performance using only one’s own body, minimal equipment, space and time. Plyometric training integrates elastic, mechanical and neurological loading properties intrinsic to the central nervous system (CNS i.e. brain power), stretch-shortening cycle (SSC) and the muscle-tendon unit (MTU) to create optimal force-velocity characteristics and muscle contraction dynamics (1). By pre-stretching an active MTU, then quickly contracting that same muscle, the SSC is able to store large quantities of energy during the eccentric (stretching) action which is then recycled in the subsequent concentric (shortening) action; thereby creating a potentiated neuromuscular response for the same operating cost (2). This ratio of metabolic effort to work output is known as mechanical efficiency and characterizes net energy utilization during all actions. Similar to a rubber band, the SSC is dependent on the magnitude and rate of MTU stretch, meaning long duration, slow stretching (i.e. static stretching) will hinder immediate energy usage. The SSC contributes most to athletic performance, when there is a timely pre-activation of musculature, a short fast, eccentric phase and a minimal transition period between muscle actions (3). Natural locomotion strategies (i.e. walking, running, throwing) inherently involve the SSC rather than isolated movement to produce power because of its increased mechanical efficiency (2). Research conducted in Kenyan elite distance runners highlights the significance of efficient SSC utilization, superior MTU stretch recoil ability, and running economy (4) . There’s also increasing evidence of SSC input in upper body actions including throwing, swimming stroke, and rowing movements (5). On the other hand, cycling is predominantly concentric in nature, therefore there is little to no active eccentric stretch, however passive elastic elements and integrated contraction dynamics will still have a small role in regulating performance. The benefit of the SSC is most significant during running, with the mechanical efficiency of positive work, or the added contribution of elasticity to be ~38-55% based on pre-stretch intensity (6). Essentially, more efficient energy storage and release allows athletes to run faster or farther for the same fat and carbohydrate breakdown, therefore preserving much needed energy during long duration events. Just three minutes of continuous SSC exercise shows significant differences in energy expenditure, but not work, in competitive versus recreational runners as a result of better mechanical efficiency and neuromuscular ability (7).

Plyometric training improves running economy:  An important determinant for LDT performance

Running economy is a well-established determinant of endurance performance, and an important differentiator of performance in elite athletes with similar maximal oxygen capacities (VO2_max) (8–10). Moreover, running economy, but not VO2_max, positively affects thermoregulatory strategies (i.e. core temperature, sweating, etc.) during bouts of running in heated climates (10). For many triathletes training to compete in Kona, the performance implications are substantial.  Interestingly, while running economy is better in runners, cycling economy seems to be less dependent on mode of endurance sport (i.e. runners, cyclists, or triathletes) (11), suggesting there may be some mechanical and metabolic cross-over between exercise modes. Running, or cycling, economy is the oxygen demand or metabolic energy required for a given work output or speed but can also be expressed as the distance for a given oxygen demand. Practically speaking, it’s functional mechanical efficiency. Improved running economy stems from a number of different physiological and biomechanical adaptations including metabolic factors and oxygen-carrying capacity, MTU stiffness, energy storage, and technical proficiency (8). Similarly, maximal swimming velocity and swimming VO2_max are primarily determined by mechanical power output and the propelling efficiency (including upper- and full-body) in elite swimmers, highlighting the importance of energy dynamics for a wide variety of human movement (12,13).

There’s substantial literary evidence demonstrating plyometric training improves running economy, primarily through better energy storage, MTU stiffness, neural input and subsequently improved force transmission (14–17). While the research is fairly convoluted, plyometric training is believed to increase MTU and joint stiffness through intrinsic changes to muscle fibre cross-bridge attachments (i.e. myofilament stiffness), CNS integration and tendinous recoil properties (i.e. elongation, elastic energy input, shortening speed)(18). The adaptations decrease the cost of moderate running speeds (8-12 km∙hr^-1) by 3.2-6.4% in ultra-endurance runners after 12 weeks of plyometric training (19). The resulting adaptations are an increased amount of energy for the same metabolic operating cost, essentially giving you free speed! Conjointly, athletes demonstrate improved time trial performance and time to exhaustion performance following plyometric only, or in conjunction with resistance training (20,21).  There’s evidence to suggest plyometric training helps to mitigate fatigue-related effects in triathletes who experience altered running patterns after a bout of cycling (22). Following plyometrics, the athlete is better able to absorb force under states of fatigue. This is particularly important for triathletes who, following high energy demands during swimming may experience reduced neuromuscular efficiency and loss of tendon recoil.  Subconsciously, this athlete will alter neural firing rate, and recruit compensatory muscles and joints, in attempts of maintaining work, thereby requiring greater contributions of fat and carbohydrate stores, affecting subsequent cycling and running performance.

Plyometrics and swimming: Useful?

Plyometric training may have particularly interesting adaptations in swimming performance, by improving neural drive in posterior shoulder muscles that stay active through the majority of the front crawl stroke (23). Although researched to a lesser extent in endurance athletes, upper body plyometrics show improved strength, power, neuromuscular adaptations in competitive adolescent swimmers (including improved 400-m performance), professional volleyball players, rugby players, and karate athletes (24,25). Seeing as mechanical power and propelling efficiency are important factors in swimming performance, there may be scope to include some plyometric training concurrently with endurance-based training. For those of us currently in lockdown, this may be an avenue worth exploring.

How do I do plyometrics?

Plyometric training exercises span from child-like jump rope exercises to the intensive metre-high shock-inducing drop jumps that most people think of, and they all have their place. However, the law of progressive overload still applies, so while you might be an experienced endurance athlete, don’t head straight to the most difficult exercise just yet. There’s indication to say training above your mechanical limits may cause more harm than good. Critical variables to consider first and foremost are intensity, volume, and periodization which will all affect your exercise choice. So, let’s get started.

Intensity

Plyometric intensity is based on three factors:

• Impact velocity
• Load distribution
• Time on the ground

Impact velocity

Impact velocity is dependent on the landing position relative to take-off.  Landing surfaces that are higher than your take-off point (i.e. box/ stair jumps), will have relatively low impact velocity because you’re having to fight gravity. These jumps thus focus on propulsive power. On the other hand, landing surfaces that are lower than your take-off point will increase the impact velocity, affecting force absorption (i.e. box drops). The latter will always be more stressful on the system; the higher the fall, the greater the eccentric velocity, tendon recoil and use of SSC, so long as the athlete has structural capacity to absorb forces! Jumps that start and end in the same position (i.e. countermovement jump; hops) integrate both phases, thus speed is critical. Accordingly, horizontal, lateral, and vertical forces will impact velocity as well. As we’re always regulated by vertical forces (i.e. gravity), multi-directional jumps will be more stressful due to additional forces.

Load distribution

Load distribution is determined by the surface at impact, affecting coordinative demands. The more limbs in contact with the ground, the less force each joint has to absorb, and the easier it is to balance. Exercise variety is going to be an important consideration for improving neuromuscular efficiency and motor programs because bilateral, single-leg, and multi-directional jumps will challenge the MTU stiffness, coordination, and neural demands differently. Bilateral jump variations will be the least stressful, then alternating or split stance jumps, with unilateral jumps being the most difficult. Similarly, upper body plyometrics follow the same rules. A plyometric push-off the wall using both arms will be the least stressful as there is very little force absorbed through the shoulder. As you become more horizontal, the impact velocity and force absorbed through the shoulders increases. Single-arm varieties will further increase load distributed through that shoulder joint and core musculature. Work just within strength limits for the greatest benefit.

Time on the ground

Finally, the time on the ground determines how intense the jump is. Reducing the time on the ground means the athlete has to absorb the same amount of forces in less time, thereby relying on their SSC to a greater extent. Accordingly, both countermovement and drop jump protocols improve running performance but the drop jump may demonstrate a greater benefit due to more similar kinematic characteristics, ground contact times and stretch rates (16). 

Volume and Periodization

If you’re just starting out with plyometrics, the low-intensity continuous jumps that we think of as “childish” are a great starting point for getting your rhythm, improving neural feedback loops, and improving mechanical efficiency. Good “startup” exercises for the lower body include:

• Hops (both single and double-legged (@ 1:06 min of video)
• Skips (@ 55 sec of video)
• Alternating box taps (@ 10 sec of video)

As a bonus, this kind of training won’t inhibit your current training too much, while letting you increase the “mileage” of your plyometric stress tolerance.

Due to coordinative demands and novelty of stress, generally perform plyometrics fresh. Add these to your routine 3-4 times weekly as a warm-up to your low-intensity day. These should mostly be time-based, focused on rhythm stiffness and coordination. Start out with 20-30s per exercise, and when it feels easy and “springy” work up from there. Focus on quality over quantity, so if you feel yourself getting uncoordinated, stop and add another set to increase work capacity. For bilateral hops, quickly flexing ankle joints after each jump will increase stiffness prior to ground contact, making it feel effortless.

For upper body some great startup exercise include:

• Plyo push-ups (@ 22 sec of video)
• Inverse rows (@ 1:44 min of video)
• Pulse varieties (@ 33 sec of video)
• Med ball variations (velocity is key!) (@ 1:32 min of video)

Both upper and lower-body varieties need to be completed quickly for optimal SSC utilization. Frequency and quality trump quantity, but like endurance volume, these need to be progressed over time, either in volume, or preferentially, difficulty. Different exercises require different motor programs, like problem solving for your brain. For more intense varieties like drop jumps or single-leg horizontal bounds, just 6-9 reps with sufficient rest prove to be beneficial prior to high-interval training. With the higher intensity varieties, tread carefully with volume. Too much intense plyometrics too quickly may acutely inhibit cycling performance, but reduced performance is expected to recover within 48 hours.

Now you’ve understood the basics of plyometric training, in the next blog we will show you some more advanced exercises you can incorporate into your training.

If you'd like to learn more about the fundamentals of the long distance triathlon training program, check out our online course - Endure IQ LDT102: Training Program Fundamentals for Long Distance Triathlon

References

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