One thing I forgot to add: Unless you're training for a specific purpose, (Military, sports, etc) keep the weights light. Excess weight can quickly lead to joint and tendon issues, which never, ever go away. Aerobic training is best done using light weights and high, rapid reps, but keep in mind to avoid jerky movements.
Also, remember to stretch. Whatever workout you settle on, a quick aerobic warmup (light jog, treadmill, etc) for about 5-10 minutes to warm up, stretching, then workout.
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