It's literally the same.
Although the attacks were directed to different parts of Luffy's body, both utilize the same principle of muscle inflation to increase the strength and speed of the strike. In the first attack, Luffy inflated his bicep, concentrating energy for a powerful blow, while in the second attack, he inflated the leg muscle to generate a similar or equal propulsive force. Thus, both attacks harness the same energy source and technique, resulting in comparable attack power and speed.