Can Muscles Overpower Tendons? Why On-Boarding Timelines Are Important.
(Take away at the bottom!)
Here is a common scenario: Ronda Rockhopper is introduced to rock climbing in her mid thirties. She falls in love. The adrenaline, the challenge, the time with friends, she just adores it. She starts going to the gym as often as possible and pretty soon she's there 4-5 days/week in between her other commitments. She has the usual delayed onset muscle soreness (DOMS) pain that makes her smile when she wakes up the next morning and can barely move her arms, but it's that 'good' kind of pain. After a few weeks, however, a new type of pain arises - it doesn't feel 'good' and it doesn't go away after a few days. It's primarily in her joints - maybe near her elbow or shoulder. It hurts more when she is doing certain motions that she can repeat. Concerned she goes to her primary care physician who dutifully sends her to an orthopedist for an eval. Long story short? She's got inflammation of the tendons and is told she needs to lay off the activity for a month or so to let things calm down.
Boo. No more rock hopping for Ronda.
So what happened?
Ronda got strong, and by that I mean that the contractile capacity of her muscles increased. This happens a few different ways: the neurological connections between her muscles and her motor cortex were reinforced and the muscle cells themselves grew more contractile proteins and machinery to support their capacity. These two things happen at different rates. Reigning clinical experience indicates that the neurological component of strength gains can occur from a few days to a few weeks after the new loading stimuli is presented. The cellular changes to the muscle fibers take a bit longer - between 6 to 8 weeks with some variation for age and gender (and I admit this is a contested topic, some new studies are indicating it may start right away but the neurological changes sort of override the effectiveness for the first few weeks).
The problem is that the rate that muscles adapt and the rate that TENDONS adapt are different. By week 4 Ronda's force generation capacity has grown a lot. Her tendons, however, will not really begin to change until 8 weeks into the new activity(1). This linked study is a great discussion of tendon adaptation rates and how they lag behind the more metabolically active muscles.
The danger here is that since your tendons have adapted to whatever baseline level of activity you have - if you suddenly increase that load significantly with high frequency your tendons just don't have to the capacity to sustain their integrity. Something has to give.
What's the take away for adult movers?
When you're trying a new skill, a new sport, a new activity of any kind - give yourself time to get used to it. This is not a discussion of rest periods - this is a discussion of 'on-boarding' new activity. If you know your tendons won't truly start adapting until around 8 weeks into an activity, gradually build up your intensity over that time period. Provide enough stimulus that you get adequate muscle growth but shy away from overwhelming your connective tissue with unabashed enthusiasm.
It's not everyone's favorite message to hear, but it's an important one. Temper your enthusiasm at the start of an activity and you will be rewarded with a pain-free entrance into whatever new sport you're exploring.
Dr. Jaimie Harrow
1. Kubo K, Ikebukuro T, Maki A, Yata H, Tsunoda N. Time course of changes in the human Achilles tendon properties and metabolism during training and detraining in vivo. Eur J Appl Physiol. 2012;112(7):2679-91.