What Goes Under Training Kit, and When the Answer Is Nothing

Two questions cover it. Does the garment over the top already have a liner, and if not, what should the layer underneath be made of?

Many running and training shorts include a built-in brief. It is designed to be worn against skin, and wearing underwear beneath it adds a seam and a damp layer that the liner was meant to replace.

The second row is the common mistake. If the short has a liner, the liner is the underwear, and doubling up creates exactly the friction it was designed to remove.

This layer sits where sweat collects most and stays there longest. Everything the rest of the site says about cotton applies with more force.

Merino is worth knowing about for anyone training and then going straight to work: it holds odour far less than synthetics, which is the practical difference over a long day. Fibre behaviour generally is in our workout t-shirt fabric guide.

Loose boxers are the one genuinely poor choice. The fabric moves independently of both you and the short, which is the definition of a friction problem. Our chafing guide covers why.

Two waistbands stacked at the same height is uncomfortable and is what most people are actually feeling when they say a short does not fit.

• Offset the heights — the under layer lower or higher.
• Avoid two gripper strips at the same point on the skin.
• Flat, wide bands distribute pressure; thin ones dig in.
• Check under a belt if you lift with one.

Waistband construction in the outer short is covered in our gym shorts length guide.

This is the least ventilated area of your kit. Damp fabric held against skin for an hour is the same mechanism behind breakouts elsewhere.

Occlusion, warmth and time are what cause the problem, and the fix is the same: get out of damp kit quickly rather than choosing a different product. Our guide to gym skin irritation covers the mechanism, and general urologic health information is published by NIDDK, part of the National Institutes of Health.

This is the item people under-buy and over-keep. It takes the heaviest sweat load per square inch of anything you own.

One pair per training session between washes is the realistic minimum, on the same logic as the rest of the wardrobe — see our guide to how many gym clothes you need.

Same rules as everything else, with less tolerance for shortcuts because the oil load is higher.

1. Wash inside out, cool, with an enzyme detergent.
2. Never fabric softener — it seals oils into the fibre.
3. Air dry; heat destroys the waistband first.
4. Wash within a day, not at the end of the week.
5. If odour persists after a proper wash, retire it.

Why synthetics hold odour, and how to strip it, is in our gym clothes care guide.

More than fabric, and more than cut. This layer has seams running through the exact areas that move most and sweat most.

A centre seam running through the gusset is the one to avoid outright, regardless of what the fabric is. A pouch construction with the seams offset to the sides is more comfortable at any price.

One practical note on buying: this is a category where trying a single pair before committing to a multipack genuinely pays. Cut and rise vary far more between makers than the size label suggests, and a five-pack of the wrong shape is an expensive way to learn that.

The same applies to fit across brands: a medium in one maker sits an inch higher on the leg than a medium in another, and the leg length is what decides whether it rides up during a session.

1. Lined shorts need nothing underneath.
2. Unlined shorts want a fitted synthetic layer.
3. Never cotton, and never loose boxers.
4. Offset the waistbands so they do not stack.
5. Replace when the waistband stops gripping.