Muscle outlines from Body Muscles by Ivan Vulović, Apache 2.0 — regrouped and recoloured for Muscle Train.
Difficulty: Beginner/Intermediate. Category: Strength. Primary Muscles: Erector Spinae, Glutes, Core. Secondary Muscles: Shoulders, Upper Back, Hip Flexors. Equipment: Bodyweight. Movement: Alternating contralateral extension. Start on all fours, hands under shoulders, knees under hips, spine neutral. Engage your core to stabilize your spine and maintain a flat back. Level 1: Extend one leg straight back, aligning with your torso. Avoid rotation. Return to start and repeat on the other side. Level 2: Simultaneously extend opposite arm and leg, aligning both with your torso. Hold briefly, return to start, and repeat on the opposite side. Maintain a stable base by pressing firmly into your hands and knees. Keep your spine neutral; reduce range of motion if needed. Drive your extended leg backward, avoiding twisting or tilting. At full extension, reach fingers and toes as if touching walls. Synchronize arm and leg movement. Hold briefly at peak extension to maximize muscle activation.
Engage your core to maintain a neutral lower back. Keep your hips aligned and facing the floor. Perform each repetition slowly and with control. Maintain a neutral neck and gaze at the floor
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