Step 1: Understanding the question.
When we talk about working against resistance, we are typically referring to activities that require force to overcome opposition, such as lifting weights, running against the wind, or moving through water. This concept is widely discussed in the context of exercise and physical activity.
Step 2: Identifying the term.
The correct term for working against resistance is "strength training" or "resistance training." These terms refer to exercises specifically designed to improve muscle strength by working against some form of resistance.
Step 3: Conclusion.
Thus, the correct word to fill in the blank is "resistance training."