main force; core strength
Refers to the primary military unit, the strongest part of a team, or the most important resource in an organization. Often used in business and sports contexts.
The enemy's main force has assembled at the front line.
He is playing an active role as a key player on the team.
main effort; primary focus
Used when describing the central activity or emphasis of a plan, project, or policy. Common in phrases like 主力を注ぐ (pour one's main effort into).
The company is putting its main effort into developing new products.
He has become the team's key player since this season.
The company is pouring its main efforts into developing new products.
This factory's main business is exports.
The team, missing its key players, struggled.
中心 means 'center' or 'core' in a spatial or abstract sense, while 主力 emphasizes the strongest or most important functional element.
本隊 is specifically the main body of a military unit or expedition, whereas 主力 can refer to the main strength in any context.
主力 refers to the top, leading performers who drive results, while 中堅 highlights the steady, experienced core that supports the group without necessarily being the stars.
Compound of 主 (しゅ, 'main') and 力 (りょく, 'power, strength'). The reading is on'yomi.