Jump squats. Lunges. Box step-ups. Try any of those holding 10lb in each hand and you'll either slow down, drop the weight, or throw off your landing. A systematic review published on PubMed Central, covering 75 studies and over 5,000 participants, found that bodyweight training is just as effective as free weights at building real muscle strength — meaning your body alone is already a legitimate training tool. A weighted vest just adds to what's already working, keeping the resistance locked to your body through every jump and every rep, so explosive movement stays explosive