Are bikes with aggressive positions required to achieve high fitness levels when training on a bike?

Question

Are bikes with aggressive positions required to achieve high fitness levels when training on a bike?

My bike fitter claimed that a more aggressive posture is better for transferring power than a more upright position.

Janheine also agreed that a more aggressive position improves power transfer. https://janheine.wordpress.com/2018/02/12/myth-5-an-upright-position-is-more-comfortable/

If their claims were true, I would need something like a gravel, road, touring, or cyclocross bike to achieve high levels of fitness.

Interestingly, TrainerRoad doesn't seem to agree. https://blog.trainerroad.com/does-bike-geometry-affect-power-output-we-asked-an-expert/

Assuming proper fit, gearing, and training zones. If I use a city or hybrid bike, would it really keep me from pushing hard enough for fitness gains?

What if I get a hybrid bike fit instead of a road bike fit?

Imagine if Chris Froome trained on a city or Dutch bike. Could he have achieved a high VO2 max of 88.2?

Speed isn't the only benefit of fitness. Getting fit often improves our health and energy levels.

There are reasons for a more upright position such as comfort, the lack of room for an additional bike, visibility, cheaper brakes levers and shifters, more room for accessories on handlebars, better vision, room for a front basket as the handlebar needs to be higher and of the right shape to accommodate it, and even safely allowing high power output downhill. If your less expensive bike is less aggressive, you might prefer to leave it on a trainer.

Answer 1

TL;DNR - The bike you will ride most often is the bike that will get you fittest.

Fitness and power transfer are unrelated. Your bike fitter is presuming you want to make the most of the power you have, so is suggesting an aggressive position is needed. This is possibly because people who pay for bike fitting tend to also be competitive riders who want to go the fastest they can with the power they have. These customers are already close to peak fitness, so they are scratching for low single digit percentages gains in 'power to the ground' (1% faster over an hour's riding is 30 seconds – that is the difference between winning and not being in the leading peloton).

If, however, your goal is to get fitter, then a more comfortable position is arguably more suitable. The more comfortable you are, the more likely you are to ride more often and further. If the power you produce is the same on a hybrid at 20km/h as on a fitted racer at 30km, and hour of exercise produces the same results in terms of fitness, it's just that one bike lets you go further. If you are uncomfortable and quit riding the fast bike after an hour vs say an hour and five minutes on the hybrid, the hybrid will get you fitter.

As far as 'Bike fitness', training on a hybrid for a century on a racer would be unwise: your training would be sub optimal as a more upright position uses muscles differently, but that is a discussion about specific fitness vs general fitness.

How much difference it makes depends on you – some people find it demoralizing busting a gut to get 20km/h when they know they can do 30km/h on a better bike, and are better off on a faster bike. Others are happy to dial up a work output and accept the speed they get.

No one needs a 7kg $10K bike to get fit, many think they are fit because they can ride a 7kg $10K bike faster than the guy on the 20kg, $200 BSO. The industry loves selling $10k bikes, hence much of the promotional material around the need for a high end racer.

Answer 2

There is a lot to unpack here. So lets go through each

Are bikes with aggressive positions required to achieve high fitness levels when training on a bike?

There isn't a single answer because there are a lot of confounding factors

1. Every bike has a fairly wide fit window now due to the wide array of components available. A bike with a more upright position can easily be made more aggressive by things such as negative rise stems
2. What is "aggressive" differs greatly by each person. For example, a person with long legs and a short torso will find that a "regular" road bike geometry will fit more aggressively as the longer inseam effectively shortens the stack.
3. If the position is too aggressive for your flexibility, body proportions or effort, it can impede gaining fitness due to discomfort and effects on biomechanics

Ideally to gain fitness the bike needs to be comfortable and put you in a position for good biomechanics. The bike fit required to get there can differ for each person.

Why do aggressive positions exist?

I believe there are two guiding principles, one is aerodynamics, which is more important for racing against other riders, than general fitness. The other is biomechanics, which is important for fitness. As you become more fit you will find you can sustain higher power outputs. Under sustained higher outputs you will find that you will naturally want to lower your body trunk so you can use gravity to resist each pedal stroke rather than just core musculature. If you take a very upright position and try to pedal as hard as you can you will find you have to hold tightly onto the bars to resist the pedal strokes. You will also find you may start to round your back which can affect how you pedal. None of these matter on a short-term basis. However, if you want to sustain a higher power output this can be less efficient as you need to recruit more of your muscle tissues (in this case more core) to resist the pedal strokes, which can be come unsustainable over longer duration of high output.

From Myth 5: An Upright Position is Always More Comfortable:

What is important is that our positions match our power outputs. A cyclist’s upper body acts as a counterweight to the forces of pedaling. The harder we pedal, the more inclined our upper bodies should be.

That is why racing bikes have low handlebars and stretched-out positions, while on cyclotouring bikes, the bars are higher, and the riders sit more upright. The extreme are some European city bikes where the riders sit bolt-upright. On those bikes, the riders’ power output is limited, and you won’t often see them in hilly towns…

The more aggressive position allows you to cheat by using gravity to resist your pedal strokes, meaning you are using less effort to pedal and can focus more of your concentration on effective pedal strokes. This also requires good flexibility at the hips and in the thoracic region of the back, which may not always be there or may need to be worked on. Also if you looking at pro racers, their low stretched out positions are on a much more extreme side than what I am envisioning.

That all said, an aggressive position also requires constant high power output to be sustainable. If you do not ride at a high power output (e.g., you are still working on fitness) then a more aggressive position may be inappropriate. When the position is appropriate for the effort you will find that your hands become unweighted, and you have a light touch on the handle bars. If you are too aggressive for your power output you will find that you place too much weight on your hands, and you may also be straining your back as you are likely not supporting your trunk weight from your hip and core, like you do when you have a light touch.

What is the best approach

The best approach is probably first to focus on just riding what ever you have, there is probably a big fit window you can explore with your existing bike. As you gain fitness try a slightly more aggressive, stretched out positions, see how that works for you, does it make it easier or harder to ride at a higher effort level. Once you run out of fit options, then start looking at a replacement bike. By this point you will have a much better idea of the type of fit you are looking for and therefore whether or not a particular bike will be suitable.