The 'Skinny' perk will increase the training power of the speed bag by about 10%. It is possible that different things aside of random variation influence training efficiency. The gains of each machine have slight random variation of a few points. Russian exercise machines show full circles for 4 hours and last for a maximum of 7 hours, but there are only 4 different ones. All exercise machines have different runtimes, ranging from as low as 3.5 hours to as high as 7 hours. This does actually not mean that the training is less effective. Mechanically, all exercise machines except the russian show a full circle for 3 hours, after which partially filled circles are shown. After returning to the regular map, both versions of the new home feature the same selection of exercise machines, replacing your garage. After 'The Choice' one of 2 new locations are introduced, 'Prison' and 'Russia', which both offer a distinct(and in case of Russia, unique) selection of exercise machines. The first 2 locations to find exercise machines are your garage and Silver's gym, which costs 10$ each time to enter.
The main way to raise strength, agility and stamina is by training at several exercise machines(or rugs) found throughout the game.
