Title: Plyometrics for Runners

The following blog post will look into a form of exercises called Plyometrics, along with discussing the importance of this form of training for runners and running athletes.

Ky Wynne is a Physiotherapist & Exercise Scientist with a professional interest in running injuries and exercise rehabilitation. Ky currently consults out of a large multidisciplinary sports medicine private practice in Melbourne, and has experience working with a range of sports including soccer & football. He has a strong passion for continued learning, and also enjoys giving back, presenting sessional lectures at Swinburne University, delivering personal development in services, and presentations at other organizations including the APA. Ky runs an evidence-based physiotherapy and S&C blog through his website, along with a social media channel on Instagram.

Website: www.kywynne.com/blog

Instagram: www.instagram.com/kywynnephysio

WHAT ARE PLYOMETRICS?

Plyometrics are rapid, powerful and dynamic movements. These exercises involve a rapid stretching and subsequent contraction of the muscles, with the purpose of developing a forceful or powerful movement in a short window of time. These movements work via neural and musculoskeletal pathways (1, 2, 3, 4, 5, 6).

Plyometrics are often used by trainers, coaches, health professionals and athletes for development of power (3, 7, 8). It is recommended that plyometrics should form a crucial component of performance and rehabilitation programs. Furthermore, this form of training is often considered the vital link between rehab and return to performance (7). Plyometrics have also been considered a bridge between strength and speed (5). Examples of plyometric activities in the lower extremities include running, sprinting, jumping, hopping, bounding, kicking and other powerful movements (1, 2, 5, 6, 7, 8).

The use of plyometrics and maximal power training allows the athlete to stimulate high velocity movements without a deceleration phase associated with heavier/strength-style training (9). The figure (see figure 2) shows the components of force and velocity trained during differing methods. Plyometrics aim to increase the amount of force that can be exerted at high movement speeds (9). Figure-3 shows an example of a force-velocity curve. Plyometric and power training work at the upper end of the velocity component, whilst strength training often works much closer the higher ends of the force component of the cure.

Figure-2, sourced from Ebben, 2001.

Figure-3 from ref 10.

Plyometrics: Mechanism

Plyometric training exaggerates the stretch-shortening cycle (SSC), utilizing a lengthening movement (eccentric) which is quickly followed by a shortening movement (concentric) (1, 4, 5, 7). The SSC is the successive combination of eccentric (ECC) and concentric (CON) muscle actions, with the combined CON and ECC actions generating forces that are greater than a CON contraction in isolation (11, 12). The combined ECC and CON actions are common in most sporting and athletic activities (11). The plyometric movements utilize both the natural elastic components of muscles, along with the tendon stretch reflex (5). The SSC during running significantly aids movement economy. Without the elastic energy storage contribution, runners would experience a significant increase (30-40%) in oxygen consumption (13).

Plyometric movements are split into 3 distinct phases (see below):

Eccentric pre-stretch phase:

• Pre-stretch phase will enhance resultant concentric muscle contraction
• This “stretch” phase allows storage of tension/elastic energy
• Important variables: can manipulate to effect the exercise outcomes. These variables impact on the amount of energy stored during the pre-stretch phase. - Magnitude of stretch - Rate of the stretch - Duration of the stretch

Amortization:

• This is the time from cessation of eccentric pre-stretch to the onset of concentric muscle action.
• Also known as the “time to rebound”, where there is a delay between overcoming the negative work of eccentric pre-stretch and generating force production, acceleration and elastic recoil.
• Key: - A shorter amortization phase leads to a more effective and plyometric movement. This is due to stord energy being used more efficiently in transition. - A slow, or delayed amortization phase means stored energy is wasted.
• One of the primary goals of plyometric training is to decrease the amortization phase. Important: Want quick/short ground contact times during plyometric movements.

Concentric Phase:

• The resultant power production performance phase.
• Results from many interactions, including the biomechanical response that utilizes the elastic properties of the pre-stretched muscles.

(3, 7).

BENEFITS

Figure-4. Benefits of plyometric training.

• Plyometric training improves power generation (4, 7)
• Plyometrics also increases the stiffness of the muscle-tendon system (1, 4). - This allows greater and more effective storage and utilization of elastic energy, with this leading to decreased energy expenditure and ground contact time (1, 4)
• Improved endurance running performance (14, 15, 16, 17)
• Improved running economy (oxygen cost of running) (1, 2, 4, 14, 15, 17) - Muscles are able to generate more force without a proportionate increase in metabolic energy requirement (4)
• Increased sprinting speed (5, 6, 7, 8, 16, 17)
• Improved acceleration (8)
• Improved jump power and ability (5, 15, 16, 17)
• Improved agility performance (5)
• Increased bone mass and remodelling (5, 9)
• Improved connective tissue strength (9)
• Increased eccentric muscle strength (9)
• Beneficial in youth athletes (5)
• Possible reduced injury risk in sports (5)

Plyometrics for Running: Overview

Running is a dynamic, high speed activity involving single leg bounding/hopping-type movements (9). It is recommended to attempt to replicate the strength, movement and speed demands of your sport in training (9). Plyometric training more closely mimics the specificity of running than slow speed strength training, with short ground contact times. Resistance training is also a crucial part of a running training program, however is not the focus of this article.

One of the major benefits of plyometrics on running performance is through the be the improvement it elicits in running economy. Running economy is defined as the steady-state oxygen requirement for a given submaximal running speed, or simple, the oxygen cost of running (15, 18, 19). The improvements in running economy lead to a runner expending less energy or oxygen consumption at a given running speed (14). Running economy has been shown to relate strongly to running performance (14, 15, 17, 18).

It has been speculated that runners with poor economy may have a reduced ability for their musculotendinous system to store and utilized the energy produced during the eccentric components of running (15, 20, 21). The exact mechanisms that plyometric improve running economy are unknown, it is thought that increased musculotendinous stiffness allows the body to store and utilize elastic energy more effectively (4, 13, 14). It is also thought that improvements in movement and running technique, muscle strength & power, and neural mechanisms contribute to improved running economy following plyometrics (1, 4).

Assessment/Minimum Competencies:

Figure-5. Sourced from (7).

Prior to undertaking a plyometrics program it is recommended to have an assessment with a trained medical professional. You need to possess minimum levels of strength and movement control to allow a safe completion of the program without significant injury risk (7). If you or your athlete doesn’t regularly train strength or plyometrics movements, it is recommended to perform a strength cycle prior to commencing plyometrics (e.g. 6-12 weeks) (9). There are some general considerations to evaluate prior to commencement (see figure-5). Furthermore, assessment of the athlete’s age, injury history, types of injuries, warm ups, foundation strength and resistance training experience are critical (7). Consider planning and preparing the plyometric sessions, along with adequate progressions to allow load management (5). Finally, it is always important to master technique prior to adding speed, complexity or load (5). Athletes may need familiarization sessions prior to commencing the program.

FITT:

Below is an evidence-based summary of FITT principles for lower limb plyometrics (1, 3, 5, 7, 9).

Frequency: Every 2-3 days

• Per week: 2 x week recommended
• Recovery: 48-72 hours recovery needed between sessions
• Duration: Continue for between 3-12 weeks (6-12 weeks recommended)

Intensity: Between 80-300 foot contacts, depending on the athlete’s ability and exercise difficulty. Figure-6 shows an example of beginner, intermediate and advanced foot contact per session.

• 3-4 exercises
• 2-6 sets
• 5-20 jumps per exercise

Figure-6. Examples of intensities for plyometric exercises (7).

Note: gradual progression of exercise intensity is recommended

Time: 10-25minutes

• Ideally completed at the start or pre-session (e.g. pre running, pre sports training, pre weights training but after a warm up).

Type: Variety of jumping, skipping, bounding movements. These include running drills, along with box jumps. Recommended to combine vertical and horizontal jumps. See the figure (figure-7) below for more examples of easy, moderate and hard levels. Recommended to consider running movements to make the exercises specific. Furthermore, incorporate single leg exercises (when physical capacity allows) where possible due to the unilateral nature of running. Remember, technique must be mastered before progression.

Note: gradual progression of exercise difficulty is recommended.

Figure-7. Examples of lower limb plyometric exercises (7).

RESEARCH STUDIES

Plyometric training has been shown elicit significant improvements in running performance (2.6-3.9%), running economy (up to 8.1%) and sprint times (2.3-3.4%). Whilst these numbers may seem small, an ~3% improvement in your 3km running time could be significant. E.g. 3kms @ 5:00min/km pace = 15minutes. A 3% improvement = 45seconds (pace of 4:45min/km). The following examples highlight some of the research papers looking at plyometrics and running.

Example 1: (Pellegrino et al., 2016)

• Subjects: recreational runners.
• Program: Progressive 6 week program, completing 15 sessions, with foot contacts increasing from 60-228.
• Result: The program provided a 2.6% increase in 3km time trial and improved running economy compared to controls.

Example 2: (Spurrs et al., 2003)

• Subjects: recreational runners.
• Program: Progressive 6 week program, completing 2-3 sessions per week, with foot contacts increasing from 60-180.
• Result: The program provided a 2.7% increase in 3km time trial and improved running economy compared to controls.

Example 3: (Paavolainen et al., 1999)

• Subjects: elite cross country runners.
• Program: Progressive 9 week program, completing 15 sessions, with foot contacts ranging between 30-200.
• Result: The program provided a 3.1% increase in 5km time trial and 8.1% increase in running economy compared to controls. Improved 20m sprint time (3.4%) and jump power (4.6%).

Example 4: (Rimmer & Sleivert, 2000)

• Subjects: recreational rugby players.
• Program: Progressive 8 week program, completing 15 sessions, with foot contacts increasing from 80-160.
• Result: Improved 10m and 40m sprint time. Increase was greatest during the initial 10m (acceleration phase). Improvements were similar to a sprint training program, thus recommended to include both.

Example 5: (Singh & Singh, 2013)

• Subjects: male students.
• Program: Progressive 10 week program, completing 20 sessions, with foot contacts approximately 60 per session. Compared between vertical jumps, horizontal jumps, combined vertical and horizontal.
• Result: Improved 40 metre sprint time for all groups (vertical, horizontal and combined). Horizontal and combined groups produced superior results comparted to vertical.

Example 6: (Ramírez-Campillo et al., 2014)

• Subjects: moderately trained male runners
• Program: 6 week program, completing 12 sessions, with foot contacts consisting of 60 per session.
• Result: Improved 2.4km time trial (3.9%) and 20m sprint time (2.3%). Also improvements in jump power.

PLYOMETRIC EXAMPLES FOR RUNNERS

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Video here: Link = https://www.youtube.com/watch?v=de4xHxfohu8&

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