Are you sure it was tennis elbow (lateral epicondylitis) that you had? It looks to me more like something you would do to treat a triceps tendinopathy
I’m still not sure – although I had ‘classic’ tennis elbow pain, there were some subtle suggestions of ulnar nerve involvement, and certainly the triceps was very tight, which might have been a contributing factor in my case.
As a rock climber, I tended to have imbalance between biceps and triceps, so it may not be the right approach for everyone.
I found the eccentric exercise was good because, unlike wrist reverse curls with weight, or even with a light theraband, it didn’t seem to aggravate it.