Jumping Rope Builds Stamina

A friendly young guy at the boxing gym, Mike, told me he did 98 doubles (jumping rope) and is coming after my record of 150. He said he was telling me in order to motivate me, so I jokingly told him to bring it on. I assume there are many younger people at the gym who could easily do more doubles than I can, but they haven’t chosen to count their jumps. Or else they are so good at the more advanced skills that trying to do a lot of doubles doesn’t appeal to them. It seems to be my niche, whether by default or because nobody else is as good at this particular minor part of the workout.
I’ve decided to believe there’s value in it. I can use doubles to increase my aerobic/anaerobic stamina as well as the endurance of my shoulders and the core muscles that hold my body in an efficient position while jumping.
The next night at the gym, after Mike’s challenge, I did some doubles early in the workout when I was still fresh. Even though it was a weeknight, I felt rested and my feet weren’t hurting, so I decided to count doubles and see how high I could go. I got up to 171 before I stopped, my shoulders aching from twirling the rope. I continued jumping normally. It turned out there were 30 seconds or more left in the round before the stop bell rang. I was pretty breathless. The next thing I’ll try to do is continue doing double jumps for the whole three-minute round. But when I’m tired even ten seconds can last forever.
One exercise we do that I’m terrible at is try to hold a plank position, face down and supporting ourselves on elbows and toes. Julia, one of the coaches, likes this one. She’ll tell us to hold it for a minute, but I collapse after counting to only ten or fifteen. That’s usually after we’ve already done a bunch of crunches and I wonder if it would be any easier if I did it fresh. I can easily hold a side plank or a push-up top position much longer. I’m not sure why that forward plank is so much harder.
Next Wednesday night I’m going to take a CrossFit class for the first time. When I emailed the gym to ask if I could come on that night, I said I was a little intimidated. Their return email encouraged me to come but acknowledged that the workout is intimidating. I hope I can get through it without giving out completely.