Threshold is a term that can potentially have a few different meanings when talking to athletes. However, most people relate it to the intensity you can hold for about a one hour of TT. Improving wattage output at this pace will almost always relate to improved performance in races; that’s why athletes and coaches talk about it so often.
There are lots of different theories about how to improve threshold power output. How to do this most effectively is the million-dollar question. However, most involve training just below, at or just above threshold for varied amounts of time.
It’s worth noting that you probably can’t sustain more than one or two sessions per week that are targeted at increasing threshold. Training at that intensity is very demanding and can lead to fatigue if over-done – especially if you’re also doing threshold training in the pool and on the run.
A threshold session should ideally contain about 25-45mins of work around threshold intensity. When starting out, aim for closer to 25mins, broken up into blocks of 5-10mins with relatively short (3-5mins) recovery periods. Then can move up towards 45mins in 10, 15 or 20min blocks.
To extract the most from threshold sessions, you’ll need to be relatively fresh and able to hit the right numbers. If you’re tired and can’t achieve the required power output on a given day, give it a rest and try again when you’re more recovered.