Plyometrics for older athletes: the perfect strength recipe?

Sports Performance Bulletin looks at new research on the potential benefits of plyometrics strength training for older athletes

A properly constructed and implemented strength-training program can produce numerous benefits for athletic performance. The most obvious is that the increased resilience of stronger muscles can help reduce the risk of injury – both those arising from inherent weaknesses and those of strength imbalances. Another major benefit is for athletes whose sports require strength and power, or those engaging in sports, which although primarily endurance in nature, require occasional bursts of power – for example, a sprint for the finish line or a mid-race burst to break away from the pack. Even better, more recent research has established that strength training can significantly boost endurance muscle efficiency – more technically known as ‘economy’^(1-5). In short, strength-trained muscles are more efficient when working aerobically, requiring less oxygen and energy to maintain a given work output (see this article for a more in-depth discussion).

Strength matters for older athletes

Although not widely appreciated, maintaining good levels of strength becomes even more important as the years tick by – not less. Why is this? Well, research has established that unchecked, lean muscle mass decreases substantially after the age of 60⁽⁶⁾. Indeed, when the resulting strength/muscle losses become severe, this can result in profound negative health consequences that extend beyond simple loss of mobility⁽⁷⁾. On the plus side, recent studies have demonstrated beyond any doubt that resistance training is extremely beneficial for maintaining muscle strength and function in elderly individuals⁽⁸⁾. Moreover, related to the ‘muscle efficiency’ benefits mentioned above, we know that older athletes are likely to have poorer muscle economy⁽⁹⁾, meaning that strength training becomes ever more important for any sportsmen or women as they become older and who is engaging in sports where endurance is required.

Plyometrics for strength

Most studies on strength training have employed some kind of resistance training intervention – either using free weights or weight machines (see this article for a discussion about the pros and cons of machines vs. free weights). However, there are other modes of strength training known to be beneficial to athletes, one of which is ‘plyometrics’. Although coming very much to the fore again over the past couple of years, plyometrics (developed by Yuri Verkhoshansky, the former Soviet track coach/ sports scientist) has in fact been a widely-used mode of athletic strength conditioning for over 40 years.

Plyometrics uses the principle of a quick-fire action and reaction between two muscular actions – a shortening and a lengthening one. The former is known as a concentric muscular action and the latter an eccentric one. For example, in the drop/depth jump, which involves jumping from a raised platform onto the ground, upon which a rebound jump is immediately made, the muscles, ligaments and tendons surrounding the ankle, knee and hip joint will undergo a stretch (eccentric action), immediately followed by shortening (concentric action) and a release of energy. This ‘stretch-shortening cycle’ is rather like the action of a bow and arrow. The drawing of the bow is akin to the eccentric stretch and the firing of the bow (and the release of all its stored energy to the arrow) the concentric reflex. For an in-depth discussion of plyometrics training, readers are directed to this article.

What Verkhoshansky discovered was that strength, speed and power could be enhanced by plyometrics training and he also determined that the speed of any movement is key to plyometrics. For example, in the drop-jump described above, the contact phase with the ground must be kept to a minimum. Why is speed important? A lightening-quick connection between the stretch and the reflex requires considerable neural energy through the central nervous system (ie your intent to move quickly), and therefore turn on (recruit) fast-twitch muscle fibers. Basically, when you perform plyometrics strength training, you are ‘teaching’ your body to release more ‘athletic horsepower’ through faster firing muscles.

Resistance vs. plyometrics strength

Although the benefits of conventional resistance training using weights are well documented, limited improvements in functional strength - ie power and rate of force production - have been reported when exercises are typically performed at slow and controlled speeds⁽¹⁰⁾. By contrast, faster, explosive resistance exercise using weights has shown greater effects on functional performance than traditional slow-speed resistance exercise⁽¹¹⁾.

In the real world however, human locomotion rarely involves the pure concentric movements that typify most weight-training movements. Instead, it consists of rapidly coupled eccentric-concentric multi-joint muscle actions, known as stretch-shortening cycle (SSC) activities. Fast eccentric-concentric transition in a SSC movement helps subsequent power generation through storage and reutilization of elastic energy⁽¹²⁾. This suggests that the use of plyometric training (which specifically targets multi-joint SSC) in older adults, could be particularly beneficial – especially bearing in mind that as the human body ages, the utilization of elastic energy becomes gradually impaired due to neural and structural changes in older muscles⁽¹³⁾

Testing the theory

The use of plyometrics training to develop functional strength has been extensively investigated in younger adults and athletes. To date however, there has been very limited research on older subjects- one reason being a concern that this more impactful type of strength training could result in a greater injury risk. However, a newly published study has investigated exactly this topic; ie whether an age-adapted plyometrics exercise program can improve dynamic strength, jump performance and functional capacity in older subjects similarly or more than traditional resistance training⁽¹⁴⁾.

In this study, Belgian and Finnish researchers compared the effects of plyometric exercise program on power, force production, jump and functional performance to traditional resistance training and walking in older men. Importantly, feasibility was investigated – ie how well the plyometrics training was tolerated and what, if any, the increased injury risk was. Forty men (average age 69 years) were randomized to 12-weeks of one of three modes of training:

• *Conventional resistance training
• *Plyometrics
• *Walking

Regardless of their group, all the subjects exercised three times weekly on non-consecutive days over a period of 12 weeks (a total of 36 sessions). Exercise sessions were performed in small groups with of maximum four subjects and were supervised by at least one expert. In both the strength-training protocols, the exercise intensity was increased progressively every three weeks. The actual protocols were as follows:

• Conventional resistance – cycling warm up then three exercises for the lower-limb muscles were performed: the bilateral leg press and straight-legged calf raises (both performed on the plate-loaded leg press) and leg extension. These exercises were chosen because they train the muscles responsible for triple extension in the lower-limb (ie quadriceps, glutes and plantar extensors in the foot) and facilitate multi-joint movements that are crucial in daily life activities such as walking and stair climbing.
• Plyometrics – this protocol provided for a slightly different cycling warm-up to include plyometric warm-up exercises: 4 x 10m high knee skips, 4 x 10m sideways skips and 8 consecutive hops with short contact times. The core exercises consisted of three exercises, using the same muscle groups (triple extension) as above: two unilateral exercises (forward step-up/jump and lateral step-up/jump), plus one bilateral exercise – a countermovement jump (see figure 1 at end).
• Walking – The training volume was progressively increased weekly from an initial 1,000 steps per day up to a maximum of 10000 steps per walk, performed three times weekly.

Results

The main findings were as follows:

• The 1-repetition maximum (1-RM) improved significantly more in the resistance (25%) and plyometrics (23%) groups compared to the walking (3%) groups. Although the resistance group achieved slightly higher gains compared to the plyo group, this difference was not significant.
• The plyo group achieved significantly greater gains in performance when tested for functional strength – ie jump height, jump power, contraction time of jumps and stair climbing performance - compared both the walking and resistance groups (see figure 2 at end).
• In terms of feasibility, adherence to the plyo program was high (at 92%) while it was well tolerated by most (70%) of the subjects.
• More injuries were noted in the plyo group, where one subject dropped out due to knee pain and two due to calf strains. This compared with one subject who dropped out in the resistance group with low back pain and none in the walking group.
• Although sometimes reported elsewhere, the PLYO subjects in this study did not report excessive muscle soreness after training.

Practical implications for older athletes

This carefully-constructed study suggests that plyometric exercises may provide additional benefits over traditional resistance training for older athletes without compromising gains in muscle strength. In particular, ploymetrics training seems to be able to more favorably enhance functional strength and power attributes – ie by improving muscle power, jumping and stair climbing performance. Moreover, this mode of strength training seems to be feasible even for older subjects – even those with no previous history of structured strength training. Indeed, nearly all of the subjects in this study reported that they really enjoyed their plyometrics sessions!

That said, a degree of caution is warranted. The researchers noted that given the increased injury risk, a preparation phase of resistance training should be considered before introducing jumps. By using traditional resistance exercises to induce hypertrophy and maximal strength gains beforehand, unaccustomed muscles would find that the progression to explosive-type of exercises would be better tolerated. The researchers also concluded that for beginners, proper tuition and supervision is recommended in order that techniques are correct. A further recommendation was that box heights of 20–30cms are feasible for step-up jumps for older beginners, whereas higher heights are not recommended due to an increased risk of knee pain resulting from unfavorable knee-joint angles.

If you’re an older athlete and are looking to improve functional and dynamic strength, adding in some plyometrics would seem to have much to offer. Those with no strength background however are advised to perform two or three months of conventional resistance first in order to ensure the muscles undergo some preconditioning. Just remember to take it gradually and start by introducing just one short session per week; only increase the session length and frequency very gradually and progressively, and once you are sure that no injury niggles are developing! For more info on the kinds of exercises to use and how to put them together, see this article.

References

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Figure 1: Plyo exercise protocol

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Figure 2: Functional strength gains

Solid line = plyo training; dotted line = resistance training; dashed line = walking.