Why Preseason Weigh Ins Happen Twice A Day

Preseason camps in American football and other summer sports weigh athletes before and after practice. The scale is being used as a hydration instrument rather than a body composition one.

Why weight change tracks fluid

Over a single practice, changes in body mass are almost entirely water. Tissue mass does not shift meaningfully in two hours.

So the difference between the pre- and post-practice weight approximates the fluid deficit, adjusted for whatever the athlete drank during the session.

That gives staff a number instead of an impression. Two athletes who both say they feel fine may have lost very different amounts.

How individual sweat rates vary

Sweat rate differs substantially between athletes performing the same work in the same conditions, driven by body size, fitness, acclimatization and genetics.

A uniform drinking instruction therefore overshoots for some and undershoots for others, which is the reason team-wide fluid rules perform poorly.

Repeated measurement builds an individual profile, and staff can then give a specific athlete a specific target expressed in bottles rather than in generalities.

What the morning weight adds

The second weigh-in, taken before practice the next day, answers a different question: whether the athlete replaced what they lost overnight.

A single hard session producing a deficit is unremarkable. The same athlete arriving lighter three mornings running is accumulating a deficit that training will not resolve.

Comparing to a stable baseline weight established at the start of camp is what makes the trend readable, since a single morning number means little on its own.

Why gaining weight is also flagged

An athlete who weighs more after practice than before has taken in more fluid than they lost, which is a warning rather than a success.

Overdrinking during prolonged exercise can dilute blood sodium, and the resulting condition is dangerous. It occurs in athletes following well-intentioned instructions to drink constantly.

Which is why the protocol looks for deviation in both directions. The scale is checking that intake matched loss, not that it was maximized.

The limits of the method

The measurement requires consistency to mean anything. Weighing in similar clothing, after using the bathroom, and on the same scale are all necessary.

It also says nothing about electrolyte losses, which vary between athletes independently of how much they sweat. A heavy salt loser is not identified by mass alone.

And weighing athletes daily has cultural risks in sports where body image is already a pressure, which is why the framing and privacy of the process are handled deliberately.

The athlete says it came out of nowhere and they are more or less telling the truth. Bone had been failing quietly for weeks. It simply has no good way of saying so.

The sequence is well described. Repeated loading produces microcracks in the mineral matrix, which is normal and happens constantly. Remodelling clears them, in a cycle that begins by resorbing the damaged section before laying down new bone. When the rate of damage outpaces the rate of clearance, the resorption cavities accumulate, and the region becomes measurably weaker while looking, to the athlete, entirely fine. That is the middle phase, and it is invisible from the outside.

Sensation arrives late because of where the nerves are. Bone itself carries limited innervation through its substance. The rich supply sits in the periosteum, the sleeve on the outside, so pain generally begins once swelling or a developing fracture line irritates that layer. By the time a shin hurts to touch, the tissue underneath has been in trouble for some time.

Compare that to muscle, which complains the next morning, or tendon, which announces itself in the first ten minutes of a session. Bone gets no such warning system, and I think that asymmetry deserves more weight than it gets. It is the reason bone injuries are managed on the basis of history rather than symptoms, and why an athlete with two weeks of vague, diffuse shin ache who has recently doubled their running deserves a serious conversation rather than a reassurance.

The known accelerants all attack the clearance side of the equation rather than the damage side. Low energy availability suppresses the hormonal environment that bone remodelling depends on, and does so quickly. Disrupted menstrual function is a signal about bone before it is a signal about anything else. Recent illness, hard dieting, and heavy travel all count.

Which is why the highest risk athlete is rarely the one training the most. It is the one training a lot while eating too little, and the second variable is invisible on any load report.

Pain that starts diffuse and becomes a point you can cover with one finger is the sequence to know.

By then the process is nearly finished, and the question is no longer prevention.