Since Twitter is all about interacting, this can be a great opportunity to connect with your current and potential clients. Twitter can be a chance to interact with clients outside of your meeting times. You get to see what they are interested in, who they follow and what they deem important enough to retweet.
Along with getting to know your clients on a more personal level, you can also motivate them. This can be a very effective way to motivate a client. They can be having an off day and tweet about it. You now know they are having an off day and can take the occasion to motivate and encourage your client.
It can also be a form of digital accountability. Tweet directly at your clients and give them some support outside of your regular scheduled time. This will show them that you actually care about them and their health goals because you are taking time to spur them on.
Another great thing you can do for your clients over Twitter is use it for customer service. You can let people ask questions about your services or let them reschedule appointments. You can also post special offers through contests or giveaways specifically on Twitter. Tell your followers that once you hit so many total followers you will give away a month of free sessions for a random follower. Or make it a contest of who can reach their goals first. There are countless options!
While all of these things about Twitter are very applicable, the most important and applicable for you is continuing a conversation with your clients and your own promotion. Twitter enables you to have another way to get your name out there. Use it and use it to its fullest potential.