Any way to raise Franklin's strength stat faster?

Been playing the game for some time now, and have actually managed to max out the stats on each character to 100/100 for each stat, but there is one very difficult one giving me pause - Franklin's strength. While the other two can use tennis to raise it REALLY quickly, Franklin absolutely refuses to play tennis. While golf seems to be an option, playing one full round seems to only yield a very slight increase. I have heard people say to me darts will raise it but tried and found it did not.

In short, is there a way I can do this stat quicker, or am I just going to have to grind it out by getting into fist fights and/or golf?

If you want to increase Franklin's stamina by playing then take part in the triathlons around LS and Blain county. By swimming, cycling and running his stamina will increase and you will not get bored...

Stand on the roof of a bus and stomp for a few minutes... You'll have to adjust his position on the bus occasionally so as to not fall off, but because it moves so slow, it's pretty easy!