Just say no
Let's move past these tired old ideas (above image) about how to swim, ideas that never made any sense. Your arms are not meant to propel your body, it's just that simple, so just say no to arm-driven swimming. Arm-driven swimming, still widely taught, is injurious and so 1980. We can do a lot better than that. Core-driven swimming is the opposite of arm-driven swimming. In core-driven swimming your arms do as little as possible while your core muscles do as much as possible. Once you begin to swim this way, once you let large core muscles drive you forward, you'll wonder why you ever did it differently. It is, in a word, transformative.
SHORT VERSION
• Arm-driven swimmers use their arms for propulsion. Core-driven swimmers use their hips for propulsion.
LONG VERSION
• Arm-driven swimmers use small muscles high in their body (lats, shoulders, and biceps) to do a lot of work — push water with their arms. Core-driven swimmers use large muscles in the middle of their body (everything from mid-thigh to ribcage) to do a little work — rotate their hips.
• Arm-driven swimmers use their arms as long levers and concentrate large forces into their shoulders. Core-driven swimmers do not.
• Arm-driven swimmers internally rotate their shoulder with each stroke. Core-driven swimmers do not. (Internal shoulder rotation is one of the causes of shoulder injuries for swimmers.)
• Arm-driven swimmers' hands and forearms are far from their long-axis. Core-driven swimmers' hands and forearms are close to their long-axis.
• Arm-driven swimmers work the back of the stroke and have a long, difficult recovery. Core-driven swimmers give up the back of the stroke and have a short, easy recovery.
• Arm-driven swimming does not rely upon balance, posture, and alignment, they are not essential. Core-driven swimming does, they are.
• Arm-driven swimmers swim uphill. Core-driven swimmers swim downhill.
• Arm-driven swimmers have little or no hip rotation. Core-driven swimmers have tremendous hip rotation.
• Arm-driven swimmers have little or no torque. Core-driven swimmers have tremendous torque.
• Arm-driven swimmers push water, thinking the power is in their arms. Core-driven swimmers hold water, knowing all of the power is in their hips.
There is no middle ground, some of both, it's one or the other, one precludes the other.
Small muscles that do a lot of work or large muscles that do a little work, your choice, but which is sustainable, which has more potential, which is more athletic?