Physiological change that allows for greater caloric expenditure? How to increase capacity for kj expenditure?

So what is changing in your body as you get fitter that allows you to accomplish rides with greater kj expenditure? I know that as your FTP goes up your TSS stays relative to it but your kj from rides will increase.
As my FTP has increased over the year, I have maintained my weight about the same and my body fat is likely similar but what has changed that allows me to accomplish higher kj expenditures than earlier in the year? Without increasing muscle mass has the glycogen capacity of my muscles increased or is it all increased mitochondria?

As its winter base season, I am interested in achieving new highs in kj expenditure on the trainer. My current biggest trainer rides have been Dombai (1389kj) and Sandy Bay (1247kj). Looking at rides that really wore me down in the past they generally ranged from 1800kj to 3060kj (as estimated by Strava rather than power meter). Ranging from 3 hour group rides that were too hard for me and I got dropped to big 5 to 6 hour solo rides where I did my own pace but was spent by the time I got home.

My last road race of the year, I finished mid-pack with ~1650kj expended (Strava est) and felt good even though I didn’t have the repeatability to make the 2nd split that determined the front group. Where I found I was more overwhelmed were these higher kj efforts.

So wondering what is actually changing and then how best to focus on those changes in my training over the winter? I have been choosing longer but lower IF alternates for my workouts that have greater caloric expenditures, unsure if thats a wise decision or not. Have a goal to complete some >1500kj workouts on the trainer this winter like Chowchilla, Paatuut, etc.

I know the importance of nutrition and proper fuelling and while I’m probably not perfect, I am using high carb drink mixes and generally taking in carbs every 20-30 mins on these long or hard rides, workouts or races.

I mainly want to understand my physiological changes around caloric expenditure in a ride and how best to increase that capacity whether its to accomplish the 900kj an hour 2 hour rides or the 3000 kj 5 hour rides.

Assuming the answer is both but wondering if for example instead of Walker (6.3 level endurance 2h15m, 122 TSS, 0.74 IF, 1287kj) I have scheduled for this week, I should instead be doing Chowchilla (3h, 134 TSS, 0.67 IF, 1533kj).

I know that as my FTP increases so does my power targets and therefore my kj expenditure on rides so am uncertain if choosing longer workouts, with lower intensity but higher kj expenditure will negatively effect my AI FTP estimation. I feel that my stamina and my FTP are limiters (if I had a higher FTP I would not get dropped on the intense 3 hour group rides as they wouldn’t be too intense for me), if I had more stamina I could maintain an intensity for longer whether its on the 3 hour group rides or the 5 to 6 hour solo rides.

The more power you put out for longer, the more kJ you use. One Watt is just one Joule per second, or alternatively one kJ is 1000 Ws, (Watts times seconds).

So to burn more kJ, you need to either ride longer, or ride at a higher average power, or both. Typically just riding longer is easier.


Larger muscles, higher density of mitochondria …


So with no change in weight or body composition its all increased density of mitochondria.

not entirely sure what you’re trying to accomplish. Why the fixation on energy expenditure? You want to become better in races. Become faster. So you should focus on becoming faster.

It sounds you’re (still) lacking endurance/durability/fatigue resistence/“the machine”. This is mainly the result of overall training volume. “Overall” in the context of weeks and months. Volume has to be built in a sustainable way.

With many endurance related adaptions it’s simply time in the saddle. Literally the number of crank revolutions. Capillary adpations (key, key, key!) are driven by shear stress. Morphological adaptions of the heart in a similar fashion.


I do think it is almost more of endurance/durability/fatigue resistance as you say rather than FTP, I understand that FTP helps but feel like I should almost be focusing more on the other factors than the FTP. I’m not sure how to do that or how to understand what that means beyond understanding that the rides where I really felt I exceeded my fitness, came with kj expenditures that exceeded my race efforts. The riders that drop me are generally racing in a class above me.

I guess I’m trying to determine how to approach my workouts, I’m in Low Volume Trad Base Block II currently and generally adding an extra workout per week and choosing longer alternative workouts of a similar PL (higher TSS, higher kj) but these are generally lower intensity (lower IF), I’m unsure if this is the correct approach.

Trying to better understand what I am trying to illicit to better understand how to manipulate my plan/workouts to better achieve these adaptations, beyond what may be more focused on increasing my FTP. I would like the achieve both but would prefer to focus on gains in the endurance/durability/fatigue resistance beyond my FTP number in isolation.

It sounds like you know what you need to be doing…you’re just not doing it?
if you’re falling apart in longer races and/or dont have repeatability then your fatigue resistance isn’t high enough.
If you’re falling apart in 1800+kj races but only doing 1200-1500 in training, while you might be training some of the same systems, you might need to add in a single long ride a week just to get your body used to those specific adaptions >2000kjs.

Not every ride needs to be super long, but simply adding a single long ride 3-4hrs a week might be all you need to do, even at zone2 to get your body used to that kind of stress

You do need periodization, so being in a base block now is not unusual as it is the offseason for most. You cannot do high intensity all year and stay sharp. You might consider replacing one of your z2 workouts with some kind of fatigue resistance progression. SS or Threshold, but I would start with SS. Try doing 60 minutes @ 90% total by working up from say 4x15, 3x20, 2x30, 1x60. It may not be that easy so you may have to try some other interval lengths to get there, but if you can do 1x60 at 90% then you would probably feel your fatigue resistance has improved. Currently I’m doing one SS workout per week. I did 1x72 minutes at 92% this week. The rest of the week I’ll chase Maria or Coco Pace Partners for 90-120 minutes, both are in my zone 2 range. I try to get outside for 2.5-3 hours at low tempo or high Z2 once a week.

My biggest kj expenditure in a race was ~1650kj and I was able to finish strong. Its group rides with faster riders and big solo efforts where I have exceeded 1800kj and fallen apart.

Based on my FTP of 217, a >2000kj ride would be way beyond my current PL level in any area. I’m currently 6.0 in Endurance, the workout Big Mountain level 7.3 endurance, 3 hours at 0.68 IF is only 1593kj. I wouldn’t get into >1800kj rides until something like Appalachian, 3h30m, 0.68 IF, 1878kj…

Most workouts the system prescribes to me are much lower kj, for example my next on the calendar is Pioneer -1 1 hour, 0.78 IF for 584kj, I was planning to swap it out for Myrtle which is 30min longer and 844kj but a lower IF 0.73.

To get to the level of >2000kj workouts I have a long way to go, just trying to figure out the best way to work towards it because I can’t just start doing 1800-2000kj rides, I don’t think I could even finish them on the trainer and it would be a huge PL jump.

Will just going longer, addressing the stamina also address the repeatability? Or is this going to be something, else that maybe I can shift focus to in the spring?

I have a list of workouts I would like to complete over the winter that would give me some >1500kj workouts but with my plan, generally TR is assigning me ~250 TSS per week, with bumping up the time of each workout I’m hitting ~315 per week but those big workouts I would like to do are 140-150 TSS so would be huge efforts for me and still not put me that close to >2000kj.

It sounds like what I need to achieve is maybe not going to happen this year but maybe if I can work up to 1500-1600kj workouts it will be a step in the right direction.

So the stamina increase that will develop to allow these higher kj rides is mainly linked to further mitochondrial density?

Honestly you might be overthinking this mitochondria thing.
You need to look at your rides and races and honestly assess what is going on.
Are you riding too close or beyond your limits in the time leading up to you being dropped?
Is your repeatability to handle surges just not there? Do you lack a sprint so you can’t contend a group finish? Or does your positioning mean that you might be missing moves or using too much energy just to stay in the wheels.

Answer that and we can then help you close the gap.

Not sure age/experience but a 217 ftp isn’t going to get you a long way in most men’s fields, so maybe it is as simple as raising your ftp.


If you’re in a group ride/race your Strava caloric expenditure estimate is going to be significantly higher than it should be. By being in a draft, your average speed will be faster for less power. Strava doesn’t know when you’re drafting so your avg power estimate will be higher. Ipso facto so will your caloric expenditure.

1 Like

As far as FTP goes, I’m 56.5kg so 217 puts me at 3.84 W/kg, hoping to get to 4 w/kg by May when the race season starts but feel like in a road race distance 70-80km or XCO race, I have the pace to hang with the group and not fall off in the end.
I moved up to Cat B for the last race of the season and finished 7th which I was happy with, I missed a split on the last lap but was able to ride away from a group of 4 that I finished with. Not making that split was multifactorial, I was trying to ride conservatively and was tail gunning on the back the whole race (so poor position) there was an attack that split the group, I hesitated to see if anyone else would bridge the gap and when nobody did, I did (with like a 15-20 second delay). Bridged that gap with 2 other racers on my wheel at a base of a climb but then the front group attacked again, I was gassed from the bridge effort (so repeatability) and the guys that I pulled up with me didn’t have it in them, so I rode the rest of the last lap with them, another two caught up and passed our group of three in the last km, I reeled them in, passed them and then hit the finish about 50 yards ahead of them and maybe 250 yards ahead of the group I had previously been riding with but were passed by the other group of 2. I was happy with that for my first time racing in that class, as I felt I was able to ride away from those 4 others racers at the end of the last lap, despite missing ‘the selection’ as I had previously considered the 4 guys I rode away from as faster than me.

Where I feel like I am weakest is when I do group rides with the Cat A guys (I don’t race them), they can just overwhelm me from all angles at will (as they have bigger FTPs, better repeatability and better stamina). On longer rides I can maybe hold their pace for ~60km and then start falling off 2/3 of the way through the ride, sometimes it due to a repeatability effect, where I feel like keeping up on the climbs slowy erodes my ability to hold the pace and sometimes it feels like it just the amount of time trying to hold the pace (like maybe when a certain amount of kjs is exceeded a start slowing down regardless of how much I’m eating and drinking). There are also group rides that are an out an back, where the way out is like tempo, turn around and then hard effort the whole way back where the group of ~15 slowly breaks off the group on the way back till there is one solo finisher (usually one of our local Pro Conti guys) and the rest generally pull in individually one at a time afterwards, in this ride I would have been the only Cat C rider (now Cat B) but its mainly Cat A guys, so I would get peeled off first or second as without even getting a turn on the front, I fall apart due to the pace.

The thing that I was able to see comparing those races where I felt strong to the finish to those group rides that were over my head or big solo rides that had me falling apart was the estimated kj expenditure. So I was thinking I want to be able to work my way up to accomplishing higher kj expenditure workouts, instead of all these ~700kj workouts TR gives me to target a TSS of ~250 a week. I think the TR plans are focused on increasing my FTP but maybe not as focused on increasing my stamina and ability to handle big kj expenditures. I feel like the TR workouts and plan have me feeling good and well prepared for racing but I see my weaknesses in group rides with faster guys or big endurance rides.

As its base season and I’ve never done a proper base build before I have been trying to increase the amount of hours I spend on the trainer but with a similar PL, which generally means a lower IF. Not sure if that is an approach that is correct or not. Kind of thinking, more hours, more TSS rather than PL or IF.

I’m modifying my prescribed workouts from the plan to better address my perceived weaknesses but I’m not confident that my approach is correct.

If you ride longer, you have to ride at lower IF. However personally I struggle to do long enough rides indoors, so I’d try to do more 3h+ rides outdoors. Maybe up to 5 hours. IF will be much lower.

The other issue I can see that you don’t capture in the kJ figures is the amount of above-FTP work that you have to do. If you ride with people with a higher FTP, they might be riding endurance and then surge at FTP, while you ride sweetspot and surge above FTP. That is a lot more fatiguing.

IMHO, you’re focusing on the wrong things and increasing your FTP should be your focus. Even if that means gaining 10+ pounds. Unless you have very long sustained climbs that determine the race, your FTP is just too low. I’m nothing special, but my z2 during race season tops off at 230s-240s at +/- 80kg. So I can hold your VO2 max for hours and repeatedly punch much much higher. There’s just no way for you to compete against that. Your light weight will only become a factor against competition like me on climbs probably longer than at least 10 minutes. Even at 10 minutes, if there’s only a few of those I can manage and stay with the feather weights.

I’d go all in on bringing up your FTP.


How should I manipulate my assigned workouts from the plan to better focus on FTP progression?

So right now I am in Trad Base Block II, getting one SS, one Tempo and one Endurance per week. I added in the Townsend -1 as extra Endurance and swapped whatever SS workout was assigned to Glassy -1 to get an extra 30 mins longer workout and to target a weekly TSS >300 and total hours on the trainer of >6 hours.

Trad Base Block III will start in 2.5 weeks and will include 4 workouts, 1 Threshold, 2 Sweet Spot and 1 Tempo.

If I am targeting FTP how should I consider the selection of alternative workouts? Maximizing IF, TSS, hours?

I have been selecting alternative workouts that are longer in time but of similar progress level (so I don’t burn myself up) but these longer workouts come with a lower IF. These longer workouts also have a higher kj expenditure and a higher TSS. I have been targeting the higher kj expenditure because although Stravas kj estimates are likely off (as I don’t have a power meter, getting one this spring for my road race bike) I feel I crack on rides of a higher kj expenditure whether it is intensity, surges or duration, when I crack it seems to be when I exceed a level of kj expenditure >1800kj estimated.

My own theory that isn’t based in anything is that I feel like if I could hold 165 watts for >2 hours (0.76 IF with current FTP) at a Z2 RPE, I would be a lot more durable on longer group rides and long solo rides.

I only got into riding July 2020 and only started structured training in spring 2022 so don’t have a lot of time invested in my legs, so have a long way to go but I feel like I need to focus on one thing and can’t address all my weaknesses at once. Unsure of what makes sense as an area of focus right now though.

Lol I had intended to keep this thread as more general and applicable to all so it was more appealing but feel like it is shifting into another “How do I get faster?” “How do I make my FTP go from blank to blank?”.

To be honest though, aside from following my TR plan I’m not sure what to add in or how to change things to better address my own weaknesses. I figured in the base season it would be better to focus on stamina/durability over FTP but am also aware that a higher FTP will generally correlate with the ability to hold 165 watts (as example) for longer.

As I don’t want to burn myself out I only want to make slight shifts at a time but am unsure how I should be shifting things to best address my weaknesses in a more specific way than the TR plans.

How much sugar do you eat on these rides? If you crack after long rides, underfueling could be a part of the problem.

~100g of carbs per hour, 20g as solids or gel every 20 mins + a bottle with 30-65g per hour (depending on length of ride).

1 Like

When I said progression, I didn’t mean TrainerRoad Progression levels. I mean progressing the duration of an interval, which is a tactic to specifically measure your fatigue resistance. So yes, you are right, if you can hold .76 for 1 hour today and have a goal to hold it for 2 hours plus tomorrow, that would be a measurable improvement in your aerobic base. You can do similar progressions for .76, .90, or 1.0 or anything in between, but the point is you can measure that improvement. One thing I find fault with TR’s progression levels is the workouts are arguably more difficult to compare. Yes, a higher PL workout is harder than a lower level one, but the workouts can vary so much that it’s hard to say what is improving. Not to mention the intervals are generally too short to create that durability that you are looking for.

If I were you and your goal is to hold 165 watts for 2 hours then I’d build/find a progression that allows you to do that. Start with 4x30, then move to 2x60, then 1x120. Keep the recoveries short, like 3 minutes or so and just see what you can do.

And don’t be in a rush to raise your FTP. IMO it’s fake news without the durability you are looking for. Lots of people can claim a 300 watt FTP because they did a ramp test, but few can hold that FTP for any significant duration. Durability takes years to develop. Being in cycling for only 2.5 years, you need to stay patient, put in the work, work on that base so you can raise the floor. Pushing the ceiling will come.


Would you suggest its better to do it in this way (with what I am guessing would be via custom workouts, haven’t tried making these yet) versus increasing the intensity of existing workouts?

For example my peak 2 hour 5 minute power is from Sandy Bay (157 watts, 95% of 165 watts)

I have walker scheduled for this weekend, if I can recover from the flu in time but its 2 hours steady at 163 watts (no breaks or undulations) . Depending on how it goes, I’m thinking I could do it again in the future with a 1-2% increase in intensity to get 2 hours at 165-166. Walker seems to be as high as the IF goes though for Endurance workouts. I would need to move to breakthrough level Tempo stuff to exceed the 0.74 IF of Walker in terms of sustained power, like Cimmeta (which Im guessing I could probably do if I can do Walker).

For an intensity with breaks I think of Half Dome, where I have my current 30min to 1 hour power PRs from Nov 5th. In working on this power zone is sticking to 1 hour workouts okay or with a focus on “durability” should I look to do lower intensity, longer duration SS workouts? That’s kind of how I have been choosing my workouts, choosing a similar PL workout with an extra 30 mins of work and higher kj expenditure but lower IF.

Looking at SS interval workouts, it seems difficult to just progress through them in a way that is like 20 min intervals unless I made custom workouts, some are 15 min intervals, some are 10-11 min intervals and some are 25 min intervals. Should I look for flat power intervals like Spruce -2 or is something like Geiger -1 okay as well?

On my calendar I have Carson -3 coming up, level 3.1, 1 hour, 65 TSS, 0.80 IF, 573kj. If I am focusing on durability, would it make sense to do El Cajon 3.0, 1h15m, 72 TSS, 0.76 IF, 686kj instead? (ideally this would be the same progress level but the idea is two workouts with same progress level, choosing the longer one at the expense of IF but increased duration, TSS and kj).