The case for skinsuits in marathons and distance events is fairly straightforward, with objective reasons for use and subjective reasons for disuse. What set this off was a conversation that either Kipchoge or Kiptum likely would have gone under 2h at Berlin had they worn skinsuits, or at the very least tight fitting tops.
1-Aerodynamics. Pretty clear cut. At 2h marathon pace a 0.1 increase in CdA is worth nearly 2 minutes. That’s 10 years worth of world record progression. I haven’t seen data on a typical singlet and half tights v skinsuit but even if it’s only half that. There’s also few rules about aerodynamic devices in running, so open season for aero shaped hats, inserts, etc.
2-Cooling. Modern fabrics are available and used that (when wet) cool better than bare skin. Higher surface area, greater evaporation, lower albedo, etc. Could be important at upcoming races like that big one in Paris.
3-Compression/energy return. Largely unexplored. There’s reason to believe that the hysteresis losses of stretch/return on a skinsuit are comparable or less than the unreturned expense of moving short/singlet fabric out of the way for it to fall back on it’s own. Probably insignificant. But there is a possibility that with a skinsuit the fabric can be laid in such a way that the energy taken in from ground impact is returned in the stride. I have doubts, but worth looking at.
Drawbacks-
1-Uncomfortable. Ok, but not insurmountable. Train in it, get used to it. In comparison to other things done to save 1 minute this seems paltry.
2- Fashion. I don’t even know what to say. If you win it will look cool. See Jacob Ingebritsen.
Theory time-
There’s an anecdote that cycling was slow to pick up marginal gains because of the prevalence of PEDs. When you could get a 10% boost from EPO there’s not much incentive to chase down small gains in chain waxing or ribbed sleeves. Better to put your energy towards perfecting your doping scheme, biggest return on investment. Now that cycling is ostensibly cleaner, the marginal gains provide a ROI comparable to the doping practices that remain (even just making doping harder/more expensive/higher risk you can shift the equation).
Professional running has seen more EPO cases in recent years than cycling. The very nature of long distance running is more conducive to doping than cycling. Pro cyclists race from March-October and have a lot of eyes on them at all times. Peak marathon runners race 2-3 times per year and spend the rest of the year holed away at camps. There’s just so much time to use PEDs in a low risk environment and clean up prior to race day.
Just like cycling in the 90’s/00’s, why would runners chase seconds from a funny looking suit when they can bump up the PEDs to gain minutes.
Conclusion-
The driving force behind baggy clothes in running is tradition/comfort/fashion. There’s free time on the table for using skinsuits in longer running races. You already see skinsuits making their way into the 1500/3k. With the speed difference from 1500-marathon compared to the time difference there’s likely more % gain in longer races. Despite this, IMO it will probably take a generational talent making them look cool for there to be any large scale adoption.