ATL, CTL & TSB explained


I appear to have opened a bit of a can of worms with my Performance Manager (PM) graph. So, for those of you (Guy in particular) who want some more info, here’s an explanation of each of the graph elements and what they signify.

The PM attempts to provide you with an indication of Form by looking at the cumulative effects of your training stress (TSS). Form (according to Andy Coggan) can be regarded as Fitness + Freshness. You need both to perform at your best. Here’s how the elements of the PM help define your Form:

ATL – Acute Training Load represents your current degree of freshness, being an exponentially weighted average of your training over a period of 5-10 days. This period is referred to as a time constant (TC). The formula for ATL looks like this:

ATL={\displaystyle ATL_y}+\frac{(TSS-ATL_y)}{\displaystyle TC_a}

Where ATL_y = yesterdays ATL, TSS = current Training Stress Score and TC_a = your ATL Time Constant

CTL – Chronic Training Load represents your current degree of fitness as an exponentially weighted average of you training over a 42 day period. Building your CTL is a bit like putting money in your savings account. If you don’t put much in you won’t be able to draw much out at a later date. The formula for CTL looks like this:

CTL={\displaystyle CTL_y}+\frac{(TSS-CTL_y)}{\displaystyle TC_c}

Where CTLy = yesterdays CTL, TSS = current Training Stress Score and TC_c = your CTL Time Constant

TSB – Training Stress Balance. This is simply the difference between your CTL and ATL, and represents your form.


A negative TSB is indicative of a high training load, i.e. high ATL relative to CTL, such as would occur in a high load training week. Alternatively, a period of taper leading up to an event should correspond with an increasing TSB where ATL is reduced relative to the current CTL.

Where TSB is positive, there is a strong indication of good performance following a consistent period of training. To help me define instances of good performance, the black line on the graph shows my ten best 20 minute mean maximal power efforts. My best three correspond to a decreased ATL following a rest week, where TSB is recovering from -20 to +5. For the time being, as I’m still in a base/build phase, I’m looking to steadily increase my CTL in preparation for TransScotland and especially Mountain Mayhem.

More (and better) articles on this subject are available from the Cyclingpeaks website. The formulas for ATL and CTL are adapted from the LW Coaching website.

Edit (15/03/07): I’ve discovered to my suprise (and horror) that a search in Google for the the above terms brings you here before places like the Cyclingpeaks website. This short article doesn’t attempt to take anything away from the guys that designed all these clever fitness metrics, so if you’ve come to this page without having visiting Cyclingpeaks then click here. The text above gives my (abridged) interpretation to the system, and there’s no substitute for hearing it from the horses mouth 😉


Pretty Graphs


Cyclingpeaks is a pretty cool piece of software. I’ve been using it to track my training progress since last November, and its taken until now for me to know where to look to see the trends in my data. Of all the graphs that show you what you’ve done, the most difficult to comprehend is the performance manager chart.

Performance Manager - February

But now that I understand what I’m looking at, its certainly one of the most useful. This last week has seen me out a lot on the bike – I’ve turned out one of best Zone 3 watts/HR and hit my third best 20 minute mean maximal power this season. I was quite pleased, but by the weekend I had to admit that I was pretty tired. When I looked at the Performance Manager chart, I saw that my Chronic Training Load had gone up 13 points in the last 8 days, a 23% increase. So I don’t overcook things and get ill, I need to back off slightly to regain a bit of freshness and then look to build my CTL further through March before I start my speed work.

I’ve been inspired somewhat by the website of Dave Harris, another 24hr soloist from the US. Having just come back from injury, he finished 2nd behind Tinker at the Old Pueblo 24hr race. Besides having a wealth of really useful info on 24hr racing on his site, he’ll “be building CTL steadily until mid-spring when I’m back to the 120-140 levels where I prefer to be for ultra racing”. To some people its just numbers, but now that I’ve got my head around the PM chart, I reckon it’s pretty impressive.


Being a Kid Again

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Learning to ride a bike of one of those things that defines your childhood. I was very proud of the fact that I taught myself to ride, and I did it without stabilisers – a bold move at the age of 7 I thought. By freewheeling my Raleigh Tomahawk down the garden path, I measured my progress in slabs. When I’d run out of slabs (which incidentally ended at the top of a short flight of steps), I ventured out onto the road in the front of the house. As I wobbled off down the road I realised that I’d done it – I’d learnt to ride a bike.

You’d think that a set of training rollers would be straight forward enough to ride wouldn’t you?

With one hand on the bench and the other trying to control the handlebars as the bike swerved around uncontrollably beneath me, I quickly discovered there was more to it than meets the eye. After a couple of false starts, and with a little assistance from Beth I gradually got myself upright, but still with one hand firmly on the bench. Gradually as I increased my cadence I steadied myself with just my fingers until, finally, and with concentration strong enough to bend spoons, I let go of the bench, wobbled a bit and I was away. I felt 7 again – I’d learnt to ride rollers 🙂


A Lesson in Motivation

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A big part of 24 hour racing is mental strength and your capacity to tolerate the discomfort and pain that comes from riding a bike for such a long duration. Before I’d done my first 24 hour solo, a friend and soloist said to me:

“If you can do the first 20 hours you’ll be OK – it’s the last 4 hours that really hurts”

I remember being unable to comprehend what I would feel like after just 12 hours, never mind 20. But I discovered that its not so much how much your body hurts, it’s how much you think it hurts. If you can motivate yourself to stay focused on the riding you find that your body will only hurt so much.

Motivation is the key to a lot of things I guess, and maintaining it can be tricky. Last week is probably a good example with things like work, the weather, darkness and my bike all conspiring against me to some extent. But the reality is most of it could have been overcome with a little motivation. It was a bit like being in the pits at a 24hr race – you know you should be out on on the course riding your bike, because if you aren’t then you’re not making any progress.


Solar Power

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The sun appeared as a pale disc through the fog this morning. While the rest of the country was bathed in sunshine (according to the weatherman), it looked like I was going have to wait a little while before I saw any of it. My enthusiasm to get out on the bike was growing faster than the fog was clearing, so at 10.30am, I went out anyway. Trying to dress for a ride that was going to involve freezing fog and most likely brilliant sunshine later on was a bit tricky, but a combination of thick gloves, buff, windproof jacket, neoprene overshoes and ¾ length leggings seemed to work OK, even if it looked a little odd.

Once I’d finally escaped from the valley bottom, leaving behind the bitterly cold fog, I found myself beneath acres of blue sky criss-crossed with vapour trails, and not a cloud to be seen. Its been the best day we’ve had for the last two months by far, and while this winter seems to have been a struggle to get the miles down, today I felt like I could ride all day.

For the first time this training season, I completed a 5 hour road ride. With over 2000m of climbing, and 80 miles, I found form today that had previously evaded me this winter. The sun on my back gave me the strength to stay out for that extra hour, just so I could enjoy it a bit longer.


Test, testing

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I’ve been training with power now for the last year and a bit, and I must say I’ve found it pretty useful. Training with heart rate is all very well, but it tends not to reflect performance in a consistant manner if you’re a bit tired or its windy. Power on the other hand gives you an instant read-out of you output every second of every ride that is comparable with other rides irrespective of how I felt or whether it was windy or not.

In order to get the most out of power training, I need to make sure I train at the right levels, which means testing. There are two values that are most significant: lower lactate threshld and upper (or anaerobic) threshold.

The anaerobic one is easy to determine – ride as hard as you can up the longest hill you can find for 30mins, and read off your average watts. The lower one is a bit more complicated and involves measuring blood lactate at different steady state wattage values until a shift is seen in the line graph. For me, this is at 175 watts, which is OK for my weight.

Lactate Power Test

So, am I fit? Well, I think so. I’m at a good point to be at in the middle of the winter, with values not too far off my peak in the middle of the summer. Lets see where I am at the end of the winter.


A Spooky Night

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While gale force winds battered most of the rest of the UK today, it wasn’t too bad down here in Wales. Sure, it was windy with occasional very strong gusts, but it didn’t stop me from taking the ‘cross bike out for a quick spin in the forest. I never see another sole on my evening rides here, which is perhaps no great suprise. Now, I don’t normally find night riding at all intimidating, but there was something about tonight that was just a bit different.

I was reminded of a time back in my university days when I was camping with a friend up at Llyn Idwal in Snowdonia. Under what was largely a cloudless sky, there was quite a strong wind when we set camp. After cooking some tea, we sat and chatted about our days walking and planning for tomorrow. The wind had dropped to virtually nothing. Our conversations were interrupted by a strange noise coming across the lake. First it was very quiet, the sound of a light breeze, but it soon began to gather momentum and speed, and quickly turned into a loud rushing noise that sounded more like a train coming. Suddenly it struck the tent – the flysheet shook violently and the candle lantern nearly lost its light. The sound could be heard receding into the distance. It was one of the most intimidating moments I’ve ever experienced, for which we’ve found no meteorological explanation – a single and very strong wave of air had hit our tent at high speed, in complete isolation.

This evening, you’d hear the odd gust approaching, but it would often carry over my head and play in the canopy of the trees around me. Suddenly: wham! – I was hit side on by a very strong gust that nearly had me off my bike. As I listened to it whirling off into the darkness, there was a strange unearthly sensation behind it. I was left with a feeling that, despite being the only person in the forest, I was not alone.


Quiet Rewards

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I like climbs. I’ll ride along way to get to them, and today was no exception. After enduring 1.5hrs of stiff headwind, and drizzle that wouldn’t give up, I found myself at the bottom of the climb that goes from Llangadog to Brynaman – the Black Mountain. For nearly half and hour I climbed, eventually up into the cloud meeting the rain at its source. As I neared the top, I turned the last corner and with it put the wind onto my back. Then it hit me.


All I could hear was the sound of my breathing and my tires on the road. There were no voices, no far off buzz of traffic, no birds, no noise from the wind as it pushed me gently along as I rode, just silence. Its not often you “hear” silence these days, and even less so on the road. Moments like these don’t happen [to me] very often, and in an odd sort of way it felt rewarding.