Having a workout partner is a fun way to stay motivated and accountable, but it can inspire feelings of jealousy when one of you begins seeing results faster than the other one. The fault may not be entirely yours -- your workout and diet may be perfect, but genetics plays a role in your response to exercise, as well. For example, if you're fat and your partner is skinny, you may very well see muscle development first.
There are three basic body types -- endomorph, mesomorph and ectomorph, or fat, athletic and skinny. Each body type can change in appearance through diet and exercise, but if left alone, will gravitate toward its natural state. Endomorphs are soft and round with little muscle tone and generally too much fat, and ectomorphs are skinny with small muscles. Mesomorphs are what many consider ideal, with a hard, muscular body and no trouble maintaining a healthy weight.
Endomorph versus Mesomorph
If you are fat, you may be either an endomorph or a mesomorph. An endomorph is naturally chunky, but has the potential for good muscular development. If you have always had a weight problem but find yourself gaining muscle early on in your fitness routine, you are likely an endomorph. A mesomorph's natural state is generally muscular and athletic, but an unhealthy lifestyle can still cause extra pounds to show up. If you were a healthy weight as a child and developed a weight problem as you grew into your adult lifestyle, you're probably a mesomorph. Both the endomorph and mesomorph can build muscle relatively easily with regular weight training because the endomorph's natural tendency is toward bulk, and the mesomorph's natural tendency is toward athleticism. Regular weight training focuses that potential for growth to the muscles, providing the stress that forces extra calories to go toward repair and growth rather than being stored as fat.
Ectomorphs and Muscle Gain
Ectomorphs are naturally skinny and have a difficult time gaining weight. If you have always been thin and can eat everything in sight without gaining an ounce, you are an ectomorph. While you don't carry extra flab, you don't have very much muscle, either. Regular weight training will make you stronger, but you'll have a difficult time developing muscle bulk because your body's natural tendency is to move calories through your system and eliminate excess. Your fast metabolism will keep you from developing a pot belly, but it won't allow extra calories to stick around long enough to fuel muscle growth. Your training must be very focused on slow, heavy repetitions to cause as much muscle stress as possible if you are to see any muscle growth at all.
Your personality matters when it comes to training results because it dictates your approach to fitness. The endomorph tends to be relaxed and laid-back, and this attitude can lead him to not stress so much about results. The ectomorph, on the other hand, tends toward social anxiety and self-consciousness, which may lead him to notice his own flaws more readily and be harder on himself than is necessary. The mesomorph tends to succeed at fitness partly because of his attitude -- he tends to be adventurous, assertive and achievement-oriented. This leads him to work out for the sheer accomplishment of it, and the physical appearance that results is only secondary.