As in bone strength or grip?
If it's grip then you need to work on strengthening your forearms.
If it's bones then some makiwara will sort you out although this can and does take many years to take full effect.
Gelatin is unlikely to have any effect on nails, the best way to strengthen nails is to have a good diet with plenty of calcium.
With legs or fists
It is good to do crunches because it will strengthen your core and push ups are good because it will strengthen your biceps.
About the size of 2 average children fists.
Flying Fists was created in 1937.
The Bloody Fists was created in 1972.
Raging Fists was created in 1975.
The Fists of Vengeance was created in 1972.
You can strengthen your Defense. Just learn karate basics.
The word fists has one syllable.
you can,t but you can stun by attacking with your fists.
The duration of Flying Fists is 1.05 hours.