fitness versus strength

My girlfriend is very fit and could run rings around me. However, while I couldn’t even run to the fridge to get a pizza, I am (probably even allowing for bodymass) much stronger than her. What is it in body terms/muscle physiology that makes one either fit or strong, but not necessarily both?

What you do. If your girlfriend runs for exercise, her body is probably sacrificing some upper body strength in order to be a better running machine. If you do a lot of carrying or maneuvering of heavy boxes or things, your body is probably building upper body strength with no stamina, if you only use your strength for short bursts.

To my way of thinking, fitness has a more “whole body” component, while strength is pretty much confined to the musculature. In order to be fit, you need to have stamina, strength, flexibility, balance, and your head on straight. Brute strength is only a part of the whole.

ColinM and Plnnr,

I agree with what you say, but I suppose I was drifting towards asking what was actually happening when one becomes “fit”. Obviously strength can come from making more muscle mass (more fibrils or just fatter ones?), but one could have two people with the same mass of muscles, but one could run 100x further than the other. Does getting fit mean more creating enzymes to do the work, more haemogoblin to carry oxygen, larger arteries or lung area? Could one take a (hypothetical) pill and suddenly be much “fitter”? What happens when one loses fitness?

“getting fit” depends on a few things. what kind of excersise you get and genetic factors (eg what muscle types you predominantly have, sex).

males produce more testosterone which enhances muscle developement.
there are different types of muscle fibres, one kind is good for sprinters and is fast twitching. the ratio of types of muscle fibres you have determines your kind of fitness to an extent. for example Olympic 100m runners have a very high percentage fast twitch muscle fibres. Powerlifters have very few by comparison.

In the op, you are asking a bit of a comparison question - what makes you big and strong and your girlfriend small and fit?? The answer to that is genetics: namely your Y chromosone. You can’t really compare men and women for physical differences and equate it to a difference in activity or effort. You also might not be entirely correct in assuming you are strong as opposed to fit - strong compared to whom? a female 50lbs lighter than you? He he… how 'bout compared to a powerlifter the same weight as you:D?? People don’t have to be either fit or strong, in fact far too many are neither. You have to compare yourself to dozens of other guys the same age/build/condition to see where you fall on the fitness scale. In general as mentioned before, building strength has mostly to do with the amount of resistance you put your muscles through, while fitness or stamina comes from develloping a better circulatory system and becoming more efficient at using energy reserves through mostly aerobic stuff for a longer period of time. Having greater strength doesn’t make up for being overall out of shape; those 400-600lb people probly have twice the strength lighter people have in their backs/legs and some other areas, but that doesn’t make life any easier for them.

Basically strength is simply the capacity to overcome resistance. This is pretty much directly related to cross sectional area of the muscle in use. Being male you will have larger muscles and be inherently stronger than the vast majority of females while young, even if you get virtually no excercise.

“Fitness” in the sense you’re using it however refers to cardio-vascular ability. Basically its a measure of how well your body can transport nutrients and oxygen to the muscles, and take waste products and CO[sub]2[/sub] away. This is dependant on a range of factors, but in “fit” people the heart muscle is bigger and has more blood vessels feeding it meaning it can work harder and longer without tiring. The lungs also tend to be larger, and slightly more vascularised. The muscles being used are also much more highly vascularised, meaning that waste products and nutrients have far less distance to diffuse to get into the muscles cells or into the blood stream. The red blood cell count in fit people is also higher, allowing the blood to carry more oxygen and co[sub]2[/sub] per unit volume.

So basically in order to be strong you need only have large muscles, which being male you will have inherently. These muscles may tire quickly however. In order to be fit you have to condition your body to allow your muscles to do sustained work. Your girlfriend, even with smaller muscles, is able to force those muscles to keep working long after yours have fatigued and her cardio-vascular system has adapted to keep those muscles fed and clean of waste.

Actually a powerlifter would have lots of fast-twitch fibers too. Remember, fast twitch = speed and power (“anaerobic”), slow twitch = endurance (“aerobic”). A marathoner would have more slow-twitch fibers. More on these fiber types here.

Your parenthetical question is the subject of much debate. Some animals, like birds, can grow new muscle fibers (it’s called hyperplasia, btw), but the last i heard, no one’s been able to prove that humans can do it, due to the difficulty counting and tracking all the fibers. It probably does happen, but only in small amounts - unless you’re an Arnold Schwartzenegger type.

“Natural abilities are like natural plants; they need pruning by study.” – Francis Bacon