The antonyms for the phrase 'lose strength' include phrases like 'gain strength', 'improve', 'fortify', 'strengthen', 'augment', and 'bolster'. These phrases mean the opposite of losing strength and refer to boosting one's physical, emotional, or mental power. To 'gain strength' means to grow stronger or more resilient, while 'improve' means to make something better or more effective. 'Fortify' implies adding strength to something that is already there, while 'strengthen' means to enhance or make more robust. 'Augment' means to increase or enlarge, while 'bolster' refers to strengthening or supporting something through reinforcement. By using antonyms for 'lose strength,' one can communicate the opposite idea of something growing weaker or less powerful.