July was busy: we hosted my parents and some friends in Montana for the first two weeks, I traveled to Des Moines for the USATF Masters Championships, and I’m writing this on the way to Chicago for a bachelor party. With Delta on the rise and lockdowns restarting, this might have been my last chance to see friends in person for a while—I’m glad that I got my travel in now.

Goal Tracking

• 🟢 Get 1% faster. I ran a personal best of 10.79 in the 100m, achieving my goal of being 1% faster on the year!
• 🔴 50% less discretionary spending. I spent 12% more on discretionary things than my 2020 average. A big chunk of that is two flights and hotel stays in Des Moines and Chicago, but then again, my 2020 average includes travel too.
• 🟡 One hour of solitary free time a day. My work-life balance continues to be fairly good, and I’ve been spending more of my free time enjoying the outdoors and reading.
• 🟢 Twice-weekly live conversations with friends. This was mostly facilitated by friends and family visiting us in Montana, and myself traveling to Iowa and Illinois. I suspect next month will be somewhat harder.

I flew into Des Moines with just one more chance to achieve my season goal: to be 1% faster than last year. I arrived two days before the meet on Thursday—I’d planned for preliminaries on Friday, but my age group (25-29) didn’t have enough competitors to need them.

Genetics clearly influence sprint performance—but by how much? There are several ways of answering this question. First, we can look for specific genetic variants that have an impact on performance. Second, we can estimate the heritability of speed or speed-related traits like muscular strength, height, and body type with twin and family studies. Finally, we can analyze the demographics of elite and sub-elite sprinters.

Genetic variants

Most of the literature focuses on two specific mutations: the ACTN3 R557R/X and ACE I/D variants.

ACTN3

ACTN3 encodes the α-actinin-3 protein, which is mostly restricted to Type II (fast-twitch) muscle fibers. Humans with the ACTN3 557XX genotype have no α-actinin-3 at all, and in fact appear to have a higher proportion of Type I (slow-twitch) muscle fibers than ACTN3 557RX or ACTN3 557RR humans. The obvious hypothesis, then, is that 577RR athletes should be better sprinters than 577XX athletes because of the existence of α-actinin-3 and a higher proportion of fast-twitch muscle fibers.

Last week, I got my hands on a pair of New Balance’s sprint spikes for 2021, the FuelCell Sigma SD-X. Although not as hyped as Nike’s Air Zoom MaxFly, New Balance’s sprint team has been running some ridiculous times in the SD-X: Trayvon Bromell is the fastest man in the world this year, and Sydney McLaughlin set the 400mh world record wearing New Balances.

Like other super spikes, the SD-X has an extremely stiff carbon fiber plate and a layer of foam in the midsole designed to maximize energy return on the track. The foam layer makes for a taller ride than most spikes—the stack height is comparable to trainers. That said, it’s definitely not a training spike: its spikes are non-removable.

I’ve spent the last couple hours trying to rebuild my mood tracker—although notifications still work, opening the app throws the error “‘mood’ Is No Longer Available”. I think this is because I last built the app a year ago, and apps installed with a paid developer account only last for a year. (Sidenote—it’s ridiculously hard to find definitive information about this. Instead, I had to trawl through the Apple Developer Forums and Reddit to try to figure out what’s going on.)