How to build core (body) strength?

How can I build up my upper body strength?

• Ok, so I'm a lifeguard, and we had to do an inservice training session yesterday to prove we still have our skills/freshen them up, and basically I was paired with a lifeguard who wrestles and throws shotput, so he's ALL muscle and happens to be 6' tall. I'm a 115 lb 5'7" girl, so basically, I'm really tiny compared to him. My boss was watching me and I went to pull him up from the bottom in a head-arm splint hold and I couldn't make it to the top because he kept sinking. Now I'm worried I'm going to lose my job if my strength doesn't improve. My boss was nice about it and after a few tries I got it but in reality there are no re-dos when I have to save someone with a head, neck, or back injury in the water. My boss said I just needed to work on upper arm and body strength, and my question is, what can I do to build up my strength and what's the fastest method? I can lift basically anyone out of the water, even large people. It's just muscle-y/athletic men that kill me. I really don't want to lose my job, I love it... Thanks in advance

• Answer:

  lifting weights, pushups, and some sort of sit ups are best.... DONT FORGET you should consider a few factors such as your age, health, and current strength level, if you are new to exercising and haven’t really done any strength training before, it’s best to start out at the lightest weight that’s comfortable to you and work up from there.