I seem to gain and lose muscle mass very quickly- what gives?

Question

I am the type of individual that looks at myself in the mirror every morning and night briefly to make sure I am not drifting off into an undesirable body shape. Sometimes, this will warrant me exercising a lot. For example, if I run a bit and lift weights over the course of a couple weeks, I notice a very quick increase in muscle mass, which seems counter intuitive to the notion that building muscle takes time.

I do an array of comprehensive exercises and reps for weight training, and my running is intense. However, I notice that in a few weeks, once I reach a threshold, I start gaining lean mass too quickly and excessively, to the point where my shirts that fit quite loosely and are rounded around my back and shoulders. My back and shoulders seem to gain muscle mass the quickest, and I get a v-shape along my lats very quickly.

However, if work creeps up or I have a lot of tasks to do, (I know excuses aren't good) I stop working out. I lose everything in a matter of days. What's the explanation for this?

Just a brief history of me.

Medical: Genetic cause of moderate anemia, type 2 diabetes on my father's side, I am about 5' 9", 160, lean, but have latent insulin resistance (fasting around low 90s)

Diet: clean for the most part, I have a penchant for fried meats, I avoid sweets. I eat a moderate amount of protein, fruits/veggies in every meal.

Sleep: bad, I sleep 5-6 hours on weekdays and 10 on weekends. Inconsistent.

Exercise: Bimodal. Either sedentary or very intense. I try to get in something brief like 30 minutes a day on some days where I'm very busy..but these usually involve things like playing with a soccer ball around my neighbrhood or pushups/pullups..no formal cardio/weight training

Answer 1

It's more or less impossible to answer a question like this over the internet, but since you said "I lose everything in a matter of days", that gives me two possible reasons for your case right away.

The first is just the obvious answer. It's your genetics. Some people respond extremely well to exercise. Here's something by T-nation:

A landmark study by Hubal used 585 male and female human subjects and showed that twelve weeks of progressive dynamic exercise resulted in a shockingly wide range of responses. The worst responders lost 2% of their muscle cross-sectional area and didn't gain any strength whatsoever. The best responders increased muscle cross-sectional area by 59% and increased their 1RM strength by 250%. Keep in mind these individuals were subjected to the exact same training protocol.

The reasons for this aren't perfectly clear and have only been hypothesized from what I've seen. The actual genetics ranges from the number of signaling molecules, to the cell's sensitivity to the signals, to satellite cell availability, to satellite cell pool expansion, to miRNA regulation. Nutrition and optimal programming play a role in hypertrophy of course, and certain genotypes may be associated with hypertrophy too.

I could go on but to answer your question (possibly), it's just pure genetics.

Now, the second possible answer is, and I actually see this a lot in myself as well, is just good ol' plain sarcoplasmic hypertrophy (high rep work). Increasing the volume of the tissue that supplies energy to the muscle or is involved with the neural drive: Intimately involved in the production of ATP are intracellular bodies called ‘mitochondria’. Muscle fibers will adapt to high volume (and higher rep) training sessions by increasing the number of mitochondria in the cells. They will also increase the concentrations of the enzymes involved in the oxidative phosphorylation and anaerobic glycolysis mechanisms of energy production and increase the volume of sarcoplasmic fluid inside the cell (including glycogen) and also the fluid between the actual cells. This type of hypertrophy produces very little in the way of added limit strength but has profound effects on increasing strength-endurance (the ability to do reps with a certain weight) because it dramatically increases the muscles’ ability to produce ATP. So basically...doing pump work will make your muscles carry a bit more fluid.

Now, with that in mind, it's been proven, specially in untrained people (such as when you take a break from working out), that the level of fluid increase in your muscles due to this type of training, can be as large as 30% of your total muscle volume. BUT, when you stop the high rep work, your cells will adapt once again, and you will lose all of it. So maybe that's the case with you as well.