This question was asked in class last week. Our instructor indicated that this was normal, and nothing to be concerned about. However, I thought it might be helpful to explore this issue in a little more depth.
Dr. Rachel Dolhun, a VP of the Michael J. Fox Foundation, states: “People with Parkinson’s may notice that some symptoms such as tremor increase during exercise, but this doesn’t mean tremor will worsen over the long run.” Source: https://www.michaeljfox.org/foundation/news-detail.php?exercise-and-parkinson-frequently-asked-questions
That’s reassuring…but there is another point worth mentioning. It is actually quite normal for people who do not have Parkinson’s to experience muscle shaking and twitches during or after intense exercise.
A physiology professor explains in Scientific American: “…large muscles that serve gross movement–such as the gastrocnemius muscle in the lower leg–have motor units made up of motor nerves that each control 2,000 or more muscle cells. These motor units are not all excited simultaneously when a muscle is electrically excited and made to contract. … The tremendous amount of overlap between motor units gives the appearance that the muscle is contracting smoothly overall. Strenuous exercise causes some of the motor units to drop out of service because of fatigue; it is this process that is ultimately responsible for the trembling you observe.” Source: https://www.scientificamerican.com/article/why-do-muscles-tremble-af/
The good news is that this should happen less as your muscles get stronger and become more used to the exercises that affect your tremor.
However, you should also be aware that dehydration and poor nutrition can contribute to these exercise shakes. Make sure you are well hydrated before exercise, and stay hydrated during a workout to replace fluids lost to sweat. Vigorous exercise that produces heavy sweat may require that you rehydrate with a sports drink to replenish potassium, sodium and electrolytes.
With Parkinson’s, the shaking is a little bit more involved than just fatigue. Dopamine is the neurotransmitter that carries signals from the brain to initiate voluntary movement. Studies have also found that dopamine is heavily involved in the process of learning and motivation. In group exercise programs, you are often learning new movements or relearning seldom used movements.
Some studies suggest that dopamine acts as a teaching signal. Like a coach motivating his player by telling him “good job” or providing feedback on how to improve, the brain releases dopamine to help learn an activity, especially an activity involving movement.
Studies like the one described here, have focused on mice, and shown the effect of higher and lower dopamine levels in teaching activities to our furry friends.
My personal opinion is that some people may benefit from a higher dose of carbidopa/levodopa prior to vigorous exercise, or if you are finding group exercise routines difficult or tremor inducing. This is an idea you may want to discuss with your neurologist. I’m not aware of any science or studies to back this up, just my personal experience…and an observation that many preworkout supplements contain ingredients designed to increase dopamine levels.