Would repeating the maintenance plan for a period of approximately 1.5 years, testing at the end of each 12 week period, and adjusting zones as necessary be the optimal way to approach an extended period where, due to work obligations, I’d be unable to race and would require a relatively low volume training schedule? Would repeating the General Phase of a 70.3 plan yield better improvement? Or is there some custom alternative that could be repeated indefinitely?
Yes, you could do that. The Maintenance plan is 12 weeks long, so you would repeat it about 7 times.
Instead, however, I would recommend that you break up the next 1.5 years in 3 distinct seasons of about 6 months each. Even if you can’t race, set goals for yourself to accomplish for each 6 month period. Maybe run a 5k (by yourself) in a certain time, or a new bike FTP… even if you can find a local 5K, 10K to aim for at the end of every 6 months. Allow yourself to reset for 1-2 weeks after every 6-month period by taking some time off.
The general phase of a 70.3 is similar to Maintenance plan, but not the same. The Maintenance plan in 6-month blocks would be better.