When you determine the things you need to improve, use this time to concentrate on making progress. You can spend some time working on your pedaling technique, your technical skills, and your aerobic engine. The work you do in the winter is an essential part of your success next summer. The major portion of your improvement from year to year results from your winter training. A triathlete can experiment with different techniques over a 400-600m swim and compare average heart rates vs. times.
Winter is a good time to build continuous swimming endurance below threshold.
Lactate threshold heart rate in the pool can be estimated by subtracting 10 beats from cycling threshold or 20 from running threshold. Slow down or check your stroke mechanics if the alarms go off. You will be left behind if you have outstanding fitness but poor technique. It is harder to develop your technique during the season because you are concentrating on optimizing your fitness for competition. Now that your main fitness concentration is on aerobic development, you can concentrate a bit more on technique issues.