Research Roundup: Tendon Stiffness & Rate of Force Development
Based on popular demand, I'm trying out a new email series: a monthly research roundup. I'm excited for this both to share sports science updates with you as well as keeping my continuing education as a coach going.
A little bit about me if you didn't know: I have a bachelor's degree in biology and I spent 3 years after graduating working in a research lab. It was an immunology/GI lab studying a disease called eosinophilic esophagitis and I've actually been published on multiple papers! (If you're curious, this was the main paper I did work for in my time: https://pubmed.ncbi.nlm.nih.gov/31264974/)
Pictured: selfie from college organic chemistry lab 😂
All to say... I really like science and I'm always excited to apply it in my coaching and stay up to date on current research.
Onto today's topic. I'll be summarizing a lecture given by Dr. Keith Barr in an Elite Athletic Performance and Programming course by the PFSCCA.
Tendon Stiffness & Rate of Force Development (RFD)
Power is a topic that I'm often asked about as a coach. The equation of power is force times velocity; in other words, force with a speed component.
There are two ways that you can increase power. You can exert more force and/or you can exert that force faster.
To produce more force, you can increase the strength and/or the size of your muscles. To increase speed, you can take a neural approach to recruit and coordinate your muscles faster and/or you can increase the rate of force development.
Today we will be discussing the latter, the rate of force development (RFD). In the body, RFD describes the transmission of force from the muscle (where the force is developed) to the bone (where movement occurs around joints). The all-important link between the muscle and the bone is the tendon/connective tissue.
Tendon stiffness is the center of the RFD discussion.
Here is a great analogy that Dr. Barr gave when thinking about the tendon and tendon stiffness:
Say you have a big weight (the bone in this analogy) laying on your desk and you're trying to move it (the muscle). You attach it to a big elastic band (the tendon) and begin to pull.
What happens first? The elastic band begins to stretch, stretch, stretch, and then maybe the weight moves a little.
What would happen if instead you attached a rope to the weight? The rope will stretch a little, but the weight will move much faster than when you pulled it with the rubber band.
Lastly, think about if you instead attached a steel rod to this weight. As soon as you pull, the weight immediately moves.
When bringing this analogy back to connective tissue, the stiffer the tendon, the better and faster you can transfer force from the muscle to the bone.
So, that's all well and good, that means we want stiffer tendons so we can be more powerful... right?
Well, it's not all so simple. There is a balance between tendon stiffness and muscle strength. If the tendon or the muscle is too much stronger than the other, there is a weak link in the chain of force transference and an increased likelihood of injury to either the tendon or muscle.
The problem is that the modalities for training muscle strength and training tendon stiffness are at odds with each other.
As shown in Wilson et al., 1993, the best way to train power (tendon stiffness) is to train max power: performing dynamic movements at a load of 30% 1RM.
(Graph from Wilson et al., 1993)
However, the best way to train muscle strength is traditional weightlifting and only doing power training over time can decrease muscle strength.
(Graph from Wilson et al., 1993)
The solution to this conundrum is to train both... and exercise order matters.
Deutsch & Lloyd, 2008 showed that by training strength first then training power, rate of force development can still be increased.
(Table from Deutsch & Lloyd, 2008)
In conclusion: tendon stiffness matters but so does muscle strength. To keep the muscles strong without sacrificing power performance, do strength training first followed by power training.
References:
Baar, K. (n.d.). Strength Training to Improve Connective Tissue Health and Performance. Elite Athletic Performance and Programming. Retrieved January 30, 2023, from https://pfscca.com/.
Lloyd R, Deutsch M. Effect of order of exercise on performance during a complex training session in rugby players. J Sports Sci. 2008 Jun;26(8):803-9. doi: 10.1080/02640410801942130. Erratum in: J Sports Sci. 2008 Aug;26(10):1122. PMID: 18569546.
WILSON, GREG J.; NEWTON, ROBERT U.; MURPHY, ARON J.; HUMPHRIES, BRENDAN J.. The optimal training load for the development of dynamic athletic performance. Medicine & Science in Sports & Exercise 25(11):p 1279-1286, November 1993.
