Hey, thanks for your questions about your hands going numb while riding.
To start, I can say that it is a common problem for cyclists, from the frequency of times I hear variations on the complaint, and the number of times people schedule a bike fit because of it. Also, there can be a lot of different causes for the problem. Exactly what part of the hands and/or if there are particular fingers that go numb, can help determine the cause. If the cause is more localized and acute it can sometimes be resolved by addressing hand positioning and glove/bartape padding, but that’s actually rare from what I’ve seen, which is unfortunate given that changing handlebar shape or adding cushion is often what manufacturers and bike shops use as their first line of attack (often to no avail, which is why the problem is so frustrating for the suffering cyclists).
At the risk of being over-simplistic in the following discussion, I’ll address solutions more in the spirit of how you should visualize the concepts rather than getting too anatomical. It is an area of bike positioning that has less to do with “bike fit” per se, and more to do with your proprioceptive sense.
If you’ve ever gone to a yoga class, played golf, or done dead lifts in the gym, you know how there is both the ideal, platonic position/form that sets the standard for the activity, and separately, there is your role in working towards that standard. On a yoga mat, or on the greens, the reasons to get closer to the ideal are largely focused on improving your practice, or your game, respectively. In the gym or on the bike, not only does understanding of proper form help you improve, it ensures that you won’t hurt yourself.
Taking the “dead lift” comparison a little further, if your grip on the bar is wrong or your gloves inadequate you’ll probably give yourself blisters, but that penalty is literally skin-deep; if your posture or stance shows poor form, as you add more weight you may seriously injure yourself with a herniated disc or muscle tear and be out of commission. The same is true for thinking about the difference between your bike’s bartape not having enough padding in contrast to your overall positioning being chronically, fundamentally, injurious.
More often, numbness is a result not of how the hands rest on the bars and thereby compress specific nerves at the contact point, but how the entire musculoskeletal arrangement, and in particular the nerves running through the shoulders and down into the arms, are affected by the overall weight distribution and structural demands on the body.
Humor me as I get esoteric here (and again, at the risk of being over-simplistic, now in basic engineering terms...): With respect to our upper body’s role while cycling it’s important to differentiate between it functioning as a structure and as a mechanism, since it has the capacity to do both. According to the Internet (which is always correct!!!), a structure is a chain of links with no relative motion between them, while a mechanism is a chain of links that allows motion and in doing so transmits motion through the chain. Like I said in your fitting appointment, a pedaling leg essentially functions as a 4-bar linkage, but additionally the kinematic chain extends all the way to the arms and hands, with the rocking hips functioning as the fulcrum connecting the upper to lower portions. If we fix the upper end of that kinematic chain by holding the handlebar, any active pushing and pulling of the bars by the arms then maximizes the body’s role as a mechanism, leveraging the bike’s structure. When we are in mechanism mode, by definition we are transferring our energy through the kinematic chain into the bike’s drivetrain and thereby the bike’s forward movement, by activating the muscles that act on the sequence of the skeletal links that make up our limbs. Being in mechanism mode emphasizes the muscles doing their thing. You could think of it as representing the dynamic, athletic, “work-out“ aspect of riding. We often go into structure mode either intentionally to economize our energy (to help pace ourselves, etc), or unintentionally because the musculature is inherently weak or has fatigued and needs support from the skeletal structure. In structure mode the emphasis shifts to the structure itself, and the strain on it. Instead of creating energy to actively transfer down into the pedals, while in structure mode we must use our energy just to deal with the strain that the static position places on the anatomical structure and it’s contact points with the bike. If our posture or weight distribution or balance is compromised, any increase in load puts undo stress on the structure’s more susceptible elements. You had asked whether possibly the handlebar is too low, and is causing the numbness in the hands. As counterintuitive as it sounds, if we look at the bar height relative to mechanism/structure, more often than not lower is less likely to cause numbness than higher. A higher bar position ends up being more likely to actually cause numbness, joint pain, back pain, and so forth, as the more upright posture virtually imposes on the upper body a structure mode as the default, and prevents the body from shifting into mechanism mode as needed.
The penalty of having a handlebar too high is having the bike’s own structure push back or work against the rider compressively. The mental visual aid I typically use to illustrate this is that of a little child at “the adult table.”
Here are some stock photos I found online that hopefully illustrate the analogy. I like how the contrast seen between dad and son in holding the plate is almost visceral - that kid is clearly struggling!
Finally, and back to your hand numbness specifically, my thinking is that you need more time to adapt to the new flexion through the spine and torso and what that asks of your abdominal muscles and related stabilizing core muscles, compared to your prior position’s extension and it’s reliance on the back muscles. You came to cycling with the back strength and muscular development accrued through a long running history, but as discussed it’s probably working against you in cycling until the anterior muscles can rise to the new challenge.
Part of that adaptation is an involuntary physiological one, but the other part is the voluntary aspect of...you guessed it...choosing to use the upper body as mechanism rather than structure. As a mechanism, remember, the fact that you are dynamic rather than static, and are “working out” in terms of the transfer of energy as per “work’s” definition in Physics, so progress is virtually part of its definition. Yes, you may fatigue and “feel the burn” as you adapt to the workload, but all of that goes towards improvement.
Improvement may be seen in structure mode as well, but the performance outcome may be limited by the fact that less energy is generated if the kinematic chain ends at the waist.
Below are two pro team “trading card“ photos of Italian Gianluca Bortolami. He employed similar bike set-up specifications through the years, but the two photos show how his bike’s positional coordinates, and his consequent “bike fit,” can equally support his body functioning either in mechanism mode or structure mode.
A properly fitted bicycle will not determine for the cyclist whether they ride it as mechanism or structure, which demonstrates the bike’s versatility as a tool, but which also means that the responsibility of choosing the appropriate mode falls on the cyclist.
On a personal note, yesterday I did a very easy 30-mile ride on the Loop, after having ridden a very aggressive, hilly 65 miles the day before, using the same bike. On the longer and harder ride I was in the low handlebar drops the majority of the time, and fully optimizing my upper body in mechanism mode. It was a serious athletic effort but I had no complaints. Conversely, yesterday I primarily sat up and rode resting on the tops of the bars in a higher position at a “conversational” pace. While my arms weren’t fully locked, they weren’t contributing much energy either, and there was much less effort involved.
However, on that easy ride I experienced hand numbness myself. I had to shake out my hands over and over again, until finally I bothered to reposition myself back into my more lower-profile and flexed position. Then, even though I wasn’t making any effort to work any harder, shifting the load away from the structure-d upright position, and into the abdominal and core muscles, I alleviated the numbness right away. Sure, my personal example is strictly anecdotal, but you get the point....