For about three years, I had a quiet rule I never said out loud: on heavy period days, I didn't run. I'd reschedule, find an excuse, do something low-effort at home instead. It wasn't a decision I made consciously each time — it had just become the default. The anxiety of wearing pale gym leggings, the logistics of managing a tampon mid-run, the general indignity of the whole situation. It wasn't worth it. So I didn't go.
I lost roughly four to six training days a month to this. Over three years, that's a significant amount of running I didn't do. I didn't think about it in those terms at the time. I do now.
The Problem I'd Normalised
I'm a recreational runner — three or four times a week, mostly 5K to 10K distances, occasionally a half marathon when I'm feeling ambitious. Running is the thing I do for my mental health as much as my physical health. Missing sessions doesn't just affect my fitness; it affects my mood, my sleep, my general ability to function like a reasonable person.
And yet I'd accepted that a quarter of my training days were just gone. Written off. I'd tried various combinations of products — tampons plus pads, period cups, different underwear — and nothing felt secure enough to run in without constant awareness and anxiety. The mental load of managing it mid-run was exhausting in a way that defeated the purpose of going in the first place.
I'd heard about period underwear but assumed it was bulky, visible under leggings, and probably not up to the demands of actual exercise. I'd dismissed it without trying it. That was a mistake.
Why I Finally Tried the Susie
A friend who runs marathons mentioned she'd been using NIXI Body for about a year and hadn't had a single issue. She specifically mentioned the Susie — the mid-rise style, the fact that it was invisible under her running tights, the fact that she'd worn it for a full 21K without thinking about it once. That last detail was the one that got me.
I found it on ALTOE and read everything. Award-winning mid-rise design. VPL-free. Holds up to 15ml — the equivalent of 2 to 3 tampons. Specifically described as loved by runners and athletes. Invisible under gym leggings and activewear. The four-layer absorbent gusset is discreet enough that you'd never know it was there from the outside.
The fabric composition was reassuring too: 75% nylon, 25% elastane on the body — the kind of performance fabric that moves well and doesn't bunch — with a 95% cotton lining against the skin for comfort, and a waterproof TPU layer as the final barrier. This wasn't a repurposed cotton brief with an extra layer sewn in. It was engineered for the purpose.
I ordered my usual size. The product description says it runs true to size, and if in doubt, size down. I went true to size and it was exactly right.
The First Run
I wore it for the first time on day two of my cycle — deliberately the hardest test I could give it. A 7K run, moderate pace, warm morning. I wore it alone, without a tampon, which felt like an act of faith I wasn't entirely sure I was ready for.
I ran the whole 7K without thinking about it once. Not once. No awareness of the gusset, no anxiety about leaking, no need to adjust anything or check anything. I finished, stretched, walked home, and felt something I hadn't felt on a period day in years: completely normal.
The leggings were fine. No visible lines, no show-through, nothing. My friend had told me it would be invisible and she was right, but I hadn't quite believed her until I saw it for myself.
Three Months of Training Through My Cycle
That was three months ago. I now train through my entire cycle without modification. The days I used to write off are back in my schedule. I've run two 10Ks and one half marathon in the Susie — the half marathon on day three, which would previously have been completely unthinkable.
I wash it at 30 degrees as instructed, no fabric conditioner, air dry. It takes a bit longer to dry than regular underwear because of the gusset layers, which the care instructions flag honestly. I bought a second pair so I always have one available. That's the practical solution and it works perfectly.
After three months of regular washing the absorbency is unchanged. The fabric has stayed soft and the fit hasn't shifted. The waterproof layer has done its job every single time. I've had zero incidents, zero anxiety, zero skipped sessions.
The Sustainability Angle
I hadn't thought much about this before buying, but it's worth mentioning: washable and reusable means significantly less waste than disposable products. Over the course of a year, the difference is substantial. The Susie pays for itself quickly when you factor in what you'd otherwise spend on disposables, and the environmental case is straightforward. It's a better option in every direction.
What It Actually Changed
I've reclaimed roughly four to six training days a month. Over three months that's somewhere between twelve and eighteen runs I would have skipped. My fitness is better. My mood during my cycle is better — partly because exercise helps, and partly because I'm no longer spending those days feeling like my body is working against me.
That shift — from dreading period days to just getting on with things — is harder to quantify than a training metric but it's the more significant change. I feel less managed by my cycle and more in charge of my own routine. That's not a small thing.
If you've been doing what I was doing — quietly writing off days, managing around your cycle rather than through it — I'd say try this. It does exactly what it says it does. For runners especially, it's the product I wish I'd found three years earlier.
Get Yours
👉 Shop the NIXI Body Susie Black Leakproof Knicker on ALTOE
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Written by Natalie Forsythe. All opinions are her own.
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