The Monday Shakeout: Long-Term Care of Tendons in the Aging Runner
By Matthew Klein
This week Matt continues to share his research and clinical experience about aging runners and tendon health
I completed my PhD dissertation on Achilles Tendinopathy in Masters runners last year. I was fortunate to have a great set of advisors and amazing people who were willing to be subjects for my research. I am still submitting and publishing manuscripts from that data set as I look at new concepts that I am continually learning about. I am in the process of setting up the next stage of my research, which is the "What to do about it?" phase rather than the "What's going on?" piece that I did my PhD on. This will look into optimal interventions for this pathology in this age range. Rather than making you all wait for the results, I'd like to share with you the background and initial hypotheses based on clinical experience.
The Achilles tendon is the largest tendon in the human body. It is a thick band of connective tissue that connects the gastrocsoleus muscle complex to the calcaneus (heel bone) and transmits tension generated by this group. In masters runners, Achilles tendinopathy it is closely followed by hamstring tendinopathy as one of the most common injuries masters runners experience (Knobloch et al., 2008). The ability of tendons to transmit forces is mostly determined by their stiffness, while the ability to store energy for release is determined by their elasticity (Delabastita et al., 2018). The loss of stiffness and elasticity in tendons can alter the force generation capacity of musculotendinous units and may contribute to the decrease in performance capacity known to occur with aging (Narici et al., 2008). This is especially important for function during activities like running as evidence has suggested that movements that fast are mostly tendon-based movements as the muscles contract mostly isometrically (Lai et al., 2018)
While exercise can be protective against age-related changes, there is a certain loss of muscle mass, strength and power that is normal with increasing age (Power et al., 2016). There is a disproportionate amount of power loss compared to the loss of muscle mass and strength (Mitchell et al., 2012). How this contributes to tendinopathy is of interest in this population. My research found that masters runners who had Achilles tendinopathy did not have any differences in calf strength or running biomechanics compared to those who did not. The major differences were in maximal power production during hopping and rate of force development from the ankle during both hopping and running. Power and rate of force development are heavily related to the stiffness and elasticity of the tendon. There is evidence that the loss of tendon stiffness and elasticity, especially in the plantarflexors, may contribute to the excessive loss of plantarflexion function seen with age (Delabastita et al., 2018). So what do we do about this?
Both for myself (especially recently with an Achilles flare-up) and for the masters runners I work with, heavy isometrics and eccentrics have been a cornerstone of supplemental strength training. While the evidence is a bit mixed for Achilles tendinopathy younger people, that is due to the fact that most people are only looking at acute pain relief. Both types of training have been seen to have positive long-term effects, although eccentric training may have better long-term effects.
Heavy isometric training, such as pushing against an immovable object or a position like a single-leg calf raise while holding a heavy weight, may be a great way to restore some of the losses of stiffness that can occur with age. These are also a great place to start as they tend to cause less soreness and muscle damage. As I have rehabbed my Achilles tendon, I have worked up to 3-4 sets of 20-second single-leg calf raise holds off a step with a 75lb kettlebell. As the research suggests, these do not provide immediate pain relief (sometimes things get a little aggravated) but I have noticed improvements in pain and function the next day. The eccentrics, especially heavy eccentrics, are key to building stiffness into the tendon while teaching it to lengthen under tension.
My favorite have been doing 50-75lb single-leg heel drops off a step (I have mid-portion Achilles tendinopathy, so I can do more aggressive range of motion earlier compared to insertional). Most injuries occur during eccentric motions, so building resiliency during that motion is important. It also creates enough tension that over time there can be remodeling and change in the tendon. I have begun to alternate the days I do the isometrics and eccentrics with a day or two of rest a week. These have not only maintained and improved my function, but also have been surprisingly quick to help the many masters runners I work with return to running, keep running or maintain function during rehab.
The final performance piece are careful calf plyometrics. Once 8-12 weeks of heavy isometric and eccentric training have been performed, one can begin training the elasticity and power back. Being able to move quick means training the tendon to act like the rubber band it is supposed to be. Double leg and single leg hops and drop jumps are a great way to train this, but given the more intense nature, less reps is better (I usually suggest 3-4 sets of 4-6 reps to focus on quality).
This trio of training interventions, with a special focus on heavy isometrics and eccentrics and a careful progression/sprinkling of plyometrics, I believe are key to maintaining and improving tendon health and function with aging.
References
Delabastita, T., Bogaerts, S., & Vanwanseele, B. (2018). Age-related changes in Achilles tendon stiffness and impact on functional activities: a systematic review and meta-analysis. Journal of Aging and Physical Activity, 27(1), 116-127.
Knobloch, K., Yoon, U., & Vogt, P. M. (2008). Acute and overuse injuries correlated to hours of training in master running athletes. Foot & Ankle International, 29(7), 671-676.
Lai, A. K., Lichtwark, G. A., Schache, A. G., & Pandy, M. G. (2018). Differences in in vivo muscle fascicle and tendinous tissue behavior between the ankle plantarflexors during running. Scandinavian Journal of Medicine & Science in Sports, 28(7), 1828-1836.
Mitchell, W. K., Williams, J., Atherton, P., Larvin, M., Lund, J., & Narici, M. (2012). Sarcopenia, dynapenia, and the impact of advancing age on human skeletal muscle size and strength; a quantitative review. Frontiers in Physiology, 3, 260.
Narici, M. V., Maffulli, N., & Maganaris, C. N. (2008). Ageing of human muscles and tendons. Disability and Rehabilitation, 30(20-22), 1548-1554.
Power, G. A., Dalton, B. H., Behm, D. G., Vandervoort, A. A., Doherty, T. J., & Rice, C. L. (2010). Motor unit number estimates in masters runners: use it or lose it?. Medicine & Science in Sports & Exercise, 42(9), 1644-1650.
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