I took vacation a couple of weeks ago, and had a lot of fun on it. That was pretty cool, and I will probably soon make a post about that, and show some cool nearby places.
I am now back to work, and so I've returned to a stricter eating and exercising regimen. Back to eating lots of cottage cheese, hitting the weights, and eliminating beer and desserts. It's all good - I was beginning to feel gross, as in nauseous most of the time...
Getting back to exercising after a couple of weeks off wasn't difficult at all. I started out at 75-90% of where I'd been and did a few extra reps. No big deal, no pain involved.
Speaking of pain, there are a couple different types of muscle pain (not associated with an injury) that you experience when you exercise.
The first of these, which is short-lived, is the burn from lactic acid. This is the intense burn you would get in your shoulders if you were to hold something heavy overhead for a while. Once the exertion stops, the pain quickly relents. The burning sensation inside the muscle is due to the buildup of lactic acid (or lactate)
Why lactic acid? The preferred energy-burning mechanism for the body is aerobic, meaning your blood is bringing sufficient oxygen to create energy from glycolysis. Glycolysis is where blood glucose is broken down (with oxygen) through a series of steps into something called "pyruvate". If enough oxygen is present, pyruvate can be further broken down for additional energy.
However, sometimes there isn't enough oxygen available for what your muscles need at that moment. Perhaps you are doing a set of heavy deadlifts or squats. Your muscles will still work, there is no way to get enough oxygen to the overtaxed muscles to continue aerobically. Having used up the available oxygenated blood, the muscles begin operating anaerobically. The pyruvate is temporarily broken down into lactic acid, which allows continued glucose breakdown and muscle use for a few minutes.
The lactic acid comes with some side effects. Because it is an acid, the muscle feels a painful burning sensation during muscle use. Additionally there are some metabolites that actually reduce muscle effectiveness. This is a handy negative feedback mechanism to keep the muscle from being damaged by longer-term oxygen deprivation.
Once the exertion stops and oxygen becomes available again, the lactic acid is re-converted to pyruvate, and the muscles can recover and resume aerobic activity.
The other type of muscle pain associated with exercise is called by an acronym, DOMS. DOMS stands for "Delayed Onset Muscle Soreness", and that's pretty self-descriptive. This is the pain that is felt in the day(s) after performing exercise, and it is not very well understood.
DOMS hits 24-72 hours after exercise, and causes a significant level of pain, as well as loss of strength and range of motion.
The generally accepted cause of DOMS is that at the cellular level, muscle fibers have been damaged by microscopic tears, and are undergoing an inflammatory response as they rebuild and repair. It is well known that eccentric weight training movements cause the most muscle damage, and are therefore the most effective for building additional muscle. Not surprisingly, eccentric movements cause the most severe DOMS.
Neither of these types of muscle pain are pleasant, but at least the lactic acid burn goes away quickly, and the DOMS is not much of an issue once you get involved in consistent exercise :)