Sub-concussive impacts can cause as much damage as a full concussion. They also accumulate to cause long term symptoms and more importantly, they are a leading cause of chronic traumatic encephalopathy (CTE). This is a atrophying of the brain that results in early onset dementia.

Sub-concussive impacts can combine to cause PCS symptoms or follow a more severe concussion and act as full concussions. I am extremely susceptible to sub-concussive impacts after a severe concussion in 1965. A sub-concussive impact while playing soccer in 1970 caused my grade points average to drop an entire grade point.

Think of this as an example. Take a hard boiled egg. You can juggle with it without breaking the shell. Once you crack the shell, you will continue to crack the shell even more by handling it with any level of intensity.

You brain is similar in structure. Once it is injured by a concussion, it become much more sensitive to lesser impacts.

The sports industry is still struggling with this concept. They are allowing full contact play after the primary concussion symptoms are gone. The only protection this affords the athlete is limited to Second Impact Syndrome where the brain has lost its ability to regulate blood pressure and can quickly become over-pressurized with possibly deadly results.

Waiting for primary concussion symptoms to resolve before returning to play does nothing to limit the chances of Multiple Impact Syndrome which is an accumulation of injury and damage from even mild sub-concussive impacts. Dr Julian Bailes is the most vocal proponent of this information.

So, sub-concussive impacts do both,. They aggravate previous symptoms than may have resolved and they cause new manifestations of symptoms. Either way, you have the cumulative effect.

I hope this explains it.

My best to you.