Well, if your goal is to
gain muscle mass, I would let up on the weight a little so you can reach muscle failure at 6-8 reps. This rep range seems to produce the best results for MOST people, because it allows you to use heavy weight, while still getting in some quality reps (enough to make you grow). Rep ranges from 1-5 usually are for strength/power training, where using near maximum to maximum weights is the goal, whereas, reps to produce more mass is usually a little higher. Reduce your weight a little and watch yourself grow!
And yah, without a spotter I would definitely limit yourself to working to just before failure on certain exercises (like bench press etc, where a spotter is crucial if you plan to hit failure on your sets).
-Todd
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