A slim figure can become strong through strength training. Strength training itself is to make muscles swell through constant congestion and muscle fiber breakage-regrowth, plus adequate and timely nutritional supplements.
According to my friend's experience, when he first entered the gym, he weighed 63KG, his arm tolerance was more than 30 CM, and his bench press was 40KG. After one and a half years, the weight was 76KG, the bench press 1 10KG, and the arm latitude was 43CM.