ElGordito wrote:
Generally related swim time improvement question that has been "weighing" on me heavily of late... I am currently at my historical weight maximum of ~180lbs which is around 10% over my weight point a few years back and roughly 20% above my "race weight" of ~145lbs back in the day (I even saw sub 140 a few times). At this weight point, I have been swimming more and focusing relatively more on my swimming (usually 3 times per week and around 9,000 total, give or take). I swam an "aerobic" 400 today in 6:10 and I would say (generally speaking) 1:25/100 is my fast 100 pace. 1:30-32/100 is my moderate pace. And 1:34-36/100 is my 1,650 pace in the pool (all SCY). So, I have wondered, if I got back down to 160-65, what kind of speed improvement could I reasonably expect, all other things being equal? Or (wishful thinking) back down to 145? Does anyone have any personal experience with the relationship between weight loss and swim speed increase in the pool over, say 4-6 months or something? Like when your technique didn't noticeably change or improve and your weekly yardage stayed pretty consistent as you lost weight from dietary modifications or increase cycling/running or other activities? If there was 10% less of me to pull, could I expect my 1:32/100 to drop a linear 10 sec/100 to ~1:23 ish? When I retired as a bike racer and rode less and ate more the following year (but was still riding some and in pretty good condition), I noticed on my favorite/main 10 min test climb, that as I gained 10% more weight from 145 to 160, my time for the same perceived hard effort went from almost always around 10 min to 11 min (exactly parallel with the weight gain).
But I'm assuming this isn't the case in the swimming pool for a variety of reasons. But I would be curious if anyone has plotted how their swim speed increased or correlated directly with weight loss (or, conversely, weight gain). In my swim "dream world", I like to imagine that if I got back to 145 lbs, my 1:32/100 pace would be all the way down to 1:12 with the same intensity (ha-ha). I'm sure just the increased drag at higher speeds would negate that kind of gain, not to mention that the swimmer's weight is supported by buoyancy, right? I have seen some rather rotund older swimmers who are still really fast in the pool most of whom were ex-collegiate swimmers. But I have never seen someone with a similar looking "beer belly" build fly up a hard climb on their bike at a comparble level. Any thoughts or data points to share?
From a standpoint of physics, in particular how the propulsive power needed to overcome dissipation scales with speed and athlete weight, a pretty solid analogy is:
cycling hills:running :: cycling dead flat:swimming
In hill cycling and running, the athlete must dominantly work to move their body weight against gravity, and speed scales inversely with body weight and linearly with propulsive power.
In (dead) flat cycling and swimming, the athlete must dominantly work against fluid dynamic form drag -- the force of this drag scales as the product of the square of the speed, the fluid density, the drag coefficient, and the frontal area. The power required to overcome this drag adds an additional factor of speed and thus scales as the cube of the speed. Drag coefficient x Frontal area, or CdA, depends weakly on weight, especially for swimming where body positioning, streamlining, and flexibility can easily overcome added pounds (see: aquatic mammals!). Speed thus scales as the cube root of propulsive power generated, as the inverse cube root of CdA, and the inverse cube root of the fluid density (air ~1000 times less dense than water -> ~10x faster).
There are (at least) a few caveats here:
i) Technique importance shares more similarity in running and swimming, since it is not so easy in either to convert work done to effective propulsive work, as it is in cycling.
ii) weight often matters even in mostly flat cycling because acceleration is a major factor in winning many types of cycling races, and the power to accelerate your body to a certain speed scales with weight. (also sprinters in grand tours need to be lean enough to make it through the mountains at all!)
iii) wave drag starts to become important at higher swim speeds, and the drag force scales even faster with speed than the square of the speed. There is nothing akin to this in cycling or running.
iv) Aerodynamic drag starts to matter for the fastest runners and limits top speeds a bit / makes it very hard to run 10m/s!