Two persons were injured when a security guard opened fire at them at Snap Fitness Centre on Vidyaranyapuram Main Road on Thursday night.
The injured are Bhaskar and Chandrashekar, a former trainer at the gym.
The police have arrested Nagaraj (62), a retired soldier, in connection with the incident.
They also seized a double-barrel gun and live ammunition from him.
Police said Chandrashekhar had left the gym recently to start one of his own. Bhaskar had come to the fitness centre to collect some money.
Nagaraj allegedly made fun of Chandrashekhar training members and this often led to frequent quarrels between them, police said.
On Thursday too, the duo argued over the matter. During the altercation, Nagaraj shot to the ground.
Bhaskar and Chandrashekar sustained injuries on their legs as the shots were fired very close to where they stood and the bullets rebounded and hit them, police said.
Bhaskar has been admitted to an hospital and Chandrasheakar was treated as an outpatient.
Vidyaranyapura police are investigating the incident.