What is a better workout: swimming longer laps, but fewer laps, or swimming shorter laps, but more laps?Couple of thoughts to share about swimming and exercise in general:
You don't tell us why you swim, which I understand can be complicated. And we usually have multiple and changing reasons. When life is hectic and stressed a standard maintenance workout can be a perfect compliment to a busy day or even for three months while your starting a new job or taking a night class. However, if you want to build strength and resilience into your body and your lifestyle strongly consider changing up your workout often.
Most people are creatures of habit and easily fall into routines, like the elderly man who walks a mile every morning. We admire and are inspired by his consistency, but your body quickly becomes accustomed to any workout you do regularly and then it flat lines and quits growing in any direction.
Everything, absolutely EVERYTHING (physical, mental, spiritual, emotional, intellectual, etc.) about the human body thrives and builds resilience with stress and rest, stress and rest. Doing the same workout, exercise, game, or job all the time is less effective, because your body gets accustom to it and isn't stressed. Cross training and doing different things with different stresses is better. Meeting and interacting with new people instead of hanging out with the same few friends. Find lots of ways to MOVE out of your Comfort Zone very often and then rest well.
I have a friend who is a little too critical to be a close friend, but he lives in another state and we did enjoy seeing him and wife a couple times a year. He always makes fun of my backyard pool as a form of exercise because it is easily traversed with a strong, well executed dive or a good push off and two strokes.
Each time he does this (I think he's jealous that we live in Florida and he doesn't), I explain again that the advantageous of swimming are the strong resistance that the water provides compared to air. Whether you overcome that resistance with arm strokes or leg push offs doesn't really matter--in fact since your arms provide about 70 percent of the power for forward motion, shorter laps with more powerful pushes again the wall is probably a better workout for your legs.
So what can you change about your workout to add a little stress. If it is Saturday and your have time, you could try doubling your workout, maybe with a break in the middle and maybe taking a rest day afterwards. Try interval swimming, swim one direction as fast as you possibly can, and the coast on the return lap to recover. How does that feel? It should be a little hard or maybe a lot hard.
Stanford University has an excellent free course on exercise physiology and how your body excels at adopting to changes in workouts, weather, altitude, etc. Here is a link: