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I'm familiar with TT and road bikes with aero bars. However, I don't know what is the ideal aero position for a normal MTB (no aero bars).

I did some search and found these pics.

Hands on the middle of handlebar mimicking position on road bikes:

Source: www.cxmagazine.com

Hands on grips, leaning forward:

Source: www.solobike.it

I asked the question because my training program says "maintain aero position for x time". Wanted to make sure I'm doing it right.

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    Can you ask the person who wrote your training program what he or she wants you to do? – R. Chung Feb 17 '16 at 4:23
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    A favorite here is palms on fork crown. I' don't recommend it. – alex Feb 17 '16 at 5:17
  • @R.Chung To be done on flat roads for endurance and anaerobic workouts – kosinix Feb 17 '16 at 5:22
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    Notice your first picture the rider is going straight forward, and in the second the rider is preparing to turn. – Criggie Feb 17 '16 at 6:21
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    Sorry, my question may not have been clear. Can you ask the person who wrote your training program what the goal of this particular training is? Are you training for a TT? Why are you doing this on a MTB, and does the person who wrote your training program know that is what you're using? Are you trying to adapt an existing training plan to that situation? – R. Chung Feb 17 '16 at 16:00
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Caveat: As mentioned by @R.Chung if you are uncertain, it is best to seek clarification from your coach. You are after all paying for their services.

Short Answer

Bike positioning is always a compromise between goals, flexibility and ability. There are different aero positions and each will have different strengths and weaknesses (see my suggestions section). I suspect the exact aero position isn't too much of a concern to your coach, rather s/he is likely interested in getting you to do efforts in a more closed position to get you prepared for riding in an aero position during a race.

What follows is a more detailed explanation.

Why train in an aero position for XC racing?

As previously stated, I suspect the coaching exercise is to get you used to working hard in a closed body position. All aero positions will get the trunk of your body lower (to reduce your frontal area, making you more slip through the air with less effort). Similar to road racing, XC racing can also be a game of marginal gains. If you can cut more drag on long flat sections than another rider, you might be able to pick up a position or maintain your positioning with less effort.

While aero positions can be useful in a race, a closed body position also affects your pedal stroke and your sustainable power output (typically reduced power) as you will be recruiting your muscle groups differently due to a different hip and back posture than you spend most of your riding hours in. If you never train in this body position, it won't be an efficient position for you to ride in come race day. Furthermore, spending time in this position it will also require you to hone your the stabilizer muscles needed to maintain that position.

In all likelihood your coach is trying to give you some training time in this type of position. The exact aero position chosen will likely not matter too much, as long as you have a closed body position so you can train muscle recruitment and stabilizers.

Some Suggestions

My suggestion (confirm with your coach) would be to try a variety of positions (the two you found pictures of is a good starting point), but stick to one aero position per interval effort. Then in each successive effort try a different posture. This will let you get a feel for how your body works.

In the two pictures you included, the first aero position one will have the lowest frontal area (aka fastest) as your arms are tucked in, but this will make the bike less stable and is likely not a good choice for rougher terrain. The second position you show sacrifices some frontal area for stability. Both have a reduced trunk angle, so both will work on your ability to recruit pedalling muscles while in a closed trunk position.

As a side note, you can also use the training time to find the best aero body trunk angle. If you go too low you will lose more power than you save in reduced drag, too little of an angle and you may still be working too hard against the wind. Keep an eye on the transect between power (if you got it), speed and heart rate to try and find the best compromise for your current flexibility and training.

The "right" compromise is very rider specific and can change over time with training.

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Depends what surface you're riding.

Aero position has more effect at higher speeds, so if you're pootling along some singletrack at 20 km/h its not worth bothering.

If you're ripping along a flat smooth offroad path at above 30 km/h then you're best having your hands wide apart to cope with anything unexpected.

The only time I'd recommend an aero "tuck" on a MTB is when its on the road, going really fast on the flat or downhill, AND you can see what's coming.

From the ground up

  1. Pedal cranks should be horizontal, one foot arch or ball on each pedal, and don't move them.

  2. Knees should be closer to the frame than normal - if its downhill you're probably not pedaling.

  3. Backside should be off the saddle and the top/rear of your thighs should be in contact with the sides of the saddle.

  4. Your backside should also be "aft" of the saddle, so any braking is assisted by weight transfer.

  5. Shoulders should be level.

  6. Head should be low as possible while still looking forward to see what's coming. Do not loose sight of the road at any time.

  7. Hands should be on the handle grips. This will give you a triangle of strength to the handlebar for steering and braking.

  8. No more than one or two fingers on the brake levers. The other two or more should be firmly on the grips.

Tyre pressure should be road levels too, not soft comfortable off-road pressures.

Some people might say move the hands towards the center of the bars for a smaller profile, and while that will help your frontal area, its a really bad idea for safety.

If your decent has corners, do slow for them in advance, using more rear brake than normal, and use weight transferrance toward the rear to keep your front brake working properly. Smooth braking is key.

Once through the corner, power on! Too many people forget to pedal on slower parts of the downhill. You can gain time this way.

I've personally done 68~69 km/h on a MTB going downhill using these techniques.

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    The question if for a training program - clearly not a coasting decent. – paparazzo Feb 17 '16 at 6:35
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    The program says "maintain aero position", nothing about pedaling. Doesn't make any sense to me, but it's a training program. – ojs Feb 17 '16 at 18:46
  • @ojs - All the pictures are of XC riders. In all likelihood the OP an endurance athlete and the coaching will be focused on endurance training. Its crazy, I know, but some people still like to ride mountain bikes both up and down mountains! – Rider_X Feb 17 '16 at 19:42
  • @ojs Comment posted 14 hours ago. "To be done on flat roads for endurance and anaerobic workouts." The original "training program says "maintain aero position for x time"". What training program would have maintain for x time if it was not a physical training program? If the training program was about aero then you would expect an explanation of aero. – paparazzo Feb 17 '16 at 20:02
  • From the comments it looks like you are confusing aerodynamic and aerobic. – ojs Feb 17 '16 at 21:03
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No one can accurately guess what your training program is asking you to do, but since we can only guess I'll offer mine.

An aero position, as typically considered, is uncomfortable for the unacquainted. An hour on a bike does not translate to an hour in aero position. In the aero position your hips will be compressed, your lungs restricted by increased tension as a result of the extreme position, your neck will be holding your head at a more severe angle, and you'll be stuck here, no moving in and out of the drops or onto bar extensions or whatever hand positions are otherwise available.

I suggest that a training program that requires an aero position is telling you to prepare your body for a rougher time. As for the specific question about getting aero on a MTB - grab the bars as close to the stem as you can, drop the elbows as low as you can, keep your back as straight as you can, and slide forward or back on the saddle to accommodate the adjustment. Oh, and aero is naturally further forward so make sure you are ready for how this impacts bike handling.

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