to strengthen
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to strengthen
To make someone or something (e.g. the body, the muscles, the economy) stronger and more resilient.
Regelmäßiges Training soll die Rückenmuskulatur kräftigen.
Regular training is meant to strengthen the back muscles.
to fortify oneself
To eat or drink something in order to regain one's strength; to strengthen oneself.
Nach der langen Wanderung mussten wir uns erst einmal mit einer Suppe kräftigen.
After the long hike, we first had to fortify ourselves with some soup.
The verb 'kräftigen' (to strengthen) is derived from the noun 'die Kraft' (strength/power). It literally means to 'make something or someone strong' or to give them strength.
Diese Übung ist gut, um die Arme zu kräftigen.
This exercise is good for strengthening the arms.
You can use 'kräftigen' transitively to make something else strong (etwas kräftigen). You can also use it reflexively when you regain your own strength (sich kräftigen).
Schwimmen kräftigt den ganzen Körper.
Swimming strengthens the whole body.
When strengthening something, typical objects are body parts such as 'die Muskeln' (the muscles), 'den Rücken' (the back), or 'das Herz' (the heart). It can also be used abstractly, for example 'das Immunsystem kräftigen' (to strengthen the immune system) or 'die Wirtschaft kräftigen' (to strengthen the economy).
Gezieltes Training kann die Bauchmuskulatur kräftigen.
Targeted training can strengthen the abdominal muscles.
to strengthen
Stärken and kräftigen can make the body or its muscles more resistant. Stärken is the usual, more broadly applicable form, while kräftigen emphasizes physical strength more specifically and sounds somewhat more formal. Use stärken in general, and kräftigen especially with the body, muscles, or a targeted physical effect.
Regelmäßiges Training kräftigt besonders die Rückenmuskeln.
Regular training particularly strengthens the back muscles.
Regelmäßiges Training stärkt den Körper.
Regular training strengthens the body.
