(Mad props to Charlotte, who asked the question that inspired this post in the comments on Monday's post.)
The common wisdom on how to achieve muscle "tone" is doing high volume work (lots of reps) at low intensity (light weight). This appears to work because, immediately after doing a workout of this nature, your muscles feel firm, even stiff.
But this immediate feeling of firmness isn't a sign that your muscles are becoming "toned." It's a sign that your muscles have used up all of their energy supply. These high-rep workouts literally tire out your muscles to the extent that they don't have enough energy to relax! The firmness you feel immediately afterwards is basically the same as rigor mortis in a corpse. That's not a good thing, and the "tone" from these workouts only lasts as long as it takes for your body to replenish the muscle's energy stores.
In fact, if you're looking for firm muscles without adding bulk, high volume, low intensity workouts are the worst thing you could do! These workouts are what bodybuilders use to build bulk via a type of muscle growth called sarcoplasmic hypertrophy, which increases the volume of fluid (called sarcoplasm) in your muscles and therefore increases muscle size without increasing "tone". (fluid isn't exactly firm...)
The best way to "tone" your muscles is to do the exact opposite of what common wisdom says to do. (Isn't that always the case?) What is commonly described as "tone" can be better defined as residual tension in a relaxed muscle. A muscle's capacity for tension corresponds to that muscle's strength. (stronger contraction = more weight lifted) So to increase the amount of tension in a relaxed muscle, you should increase the amount of tension that muscle is capable of creating. (higher capacity for tension = more residual tension when relaxed) In other words, you should make that muscle stronger.
This means that you should use high intensity, low volume workouts that build strength without inducing lots of hypertrophy. Pavel (from whom most of the ideas presented in this post are stolen) recommends 2 sets of 5 reps, using a weight that you can lift 5 times (but not 6) for the first set and 90% of that weight for the second. Rippetoe's Starting Strength program uses 3 sets of 5 with the same weight on each set. In my opinion, as long as you stay below 20 total reps in 4 or fewer sets with weights above 80% of your 1 rep maximum, you're on the road to building strength and therefore "tone" without adding bulk.
5 x 5 x 240
2 x 5 x 230
2 x 4 x 230
3 x 230
5 x 325
13, 9, 8
Overhead Decline Situps
3 x 8 x 45
Comments: Squats are actually starting to feel easier as I approach my previous workout weight, probably just because I'm getting used to them again. Bench Press regressed from last time. D'oh! If I stall, I might try switching over to 8x3 for a while to see if I can break through. Deadlift was AWESOME. It was one of those where I grinded out the 5th rep, then walked around lightheaded for half a minute before getting what I fondly think of as that "hell yeah!" feeling of accomplishment. Happy that Chinups actually improved from before the layoff. Overhead situps for torso strength and to reinforce the "head through the window" feel of Press.