Latissimus, Forearm, Trapezius, Shoulders, Chest, Triceps, Back
Use a box so you can easily set up your position.
Take a shoulder width pronated grip (palms forwards) and flex your elbows so that your chin is above the bar. Actively depress & retract your scapula (Drive your shoulder blades down & together), while pushing your chest up and forward, creating an arch shape in your upper back.
Keep your legs together, core braced and whole body tight.
Hold for time.