Question #1 for you: when I work out my arms, they fatigue very quickly! My "lifting to failure" happens pretty easily, yet I'm very rarely sore the next day. Legs, on the other hand, I feel like I can squat and lunge all day (I do get shaky) but I get SO SORE. Like I can barely move the next day. Why does this happen? One muscle group feels so strong but gets bad delayed onset muscle soreness, and the other feels much weaker, but only a little stiff? Keep in mind I do the same number of reps for each.
Second question is: any time I do an exercise where a bar is across my upper back/shoulders (squats, clean & press) where my arms have to hold the bar, my arms go horribly numb/asleep. In a group weight class, I have to shake my arms out all the time but it doesn't seem to bother other people. I've tried positioning my grip wide to narrow and it doesn't help. What is causing this? When I asked the instructor, he couldn't understand what I meant and said he'd never heard of that problem before.
The movements that you are doing for your legs (squats and lunges) involve a lot of e-centric movement and depending on the speed at which you are completing these exercises you could be challenging your legs e-centrically (which is the downward phase of the movement where you are lengthening your muscles) more than you are with your upper body.
In an e-centric movement, as your muscle lengthens it becomes weaker and therefore it is being challenged to a greater capacity than if you were to only train it concentrically (the upward phase of the exercise where your muscle is shortening). Have you ever hiked down a mountain (or hill) and wondered why you are sorer than you are when you hike up? It is because of the e-centric movement.
In your upper body exercises you might not be working as hard on the e-centric phase and allowing gravity to do the work. Next time you are at the gym try varying the speeds of your movements. For example, when doing a bicep curl try lifting the weight up in a count of one and then lowering it for a count of three. Lowering the weights at a slower pace may increase the soreness you experience the next day as you build your strength e-centrically. But understand just because you are not sore the next day does not mean your body is not seeing improvements. You are still building strength and will continue to benefit from your workouts if you continue to progress your weights and your exercises. You can also add power and plyometric exercises to your upper body routine, such as medicine ball tosses, rope work, burpee push-ups, etc.
To answer your second question, your arms are going numb because you are extremely tight through your chest, shoulders, triceps, biceps and lats. You lack the flexibility you need to put your arms into the required position to hold the bar. There are two ways to fix this. The first option is improving the flexibility and range of motion of your upper body through stretching and chest opening exercises. The second option is using wrist straps to hold the bar, which will limit the strain on your upper body.
Like you, I am very tight through my upper body as well and my arms go numb even while I blow dry my hair! So when I squat and lunge I hold dumbbells by my side for added weight or position the bar in the front of my body (front squats) so I do not have to experience the pain and numbness that goes along with having a bar on my back.
Keep up the good work and thanks for your questions!
Attached - Taylor Swift at dance practice in Los Angeles this week.