Keep your arms straight. Protract and depress your scapula, round your back, separate your shoulder blades, drive your shoulders down. Bring the knees as close to your chest as possible, maintain that positioning in the extremes of those ranges while trying to lean back and counterbalance that with pushing your hips forward as far forward as possible. This will load your upper back and tricep tremendously. Make sure to do this movement carefully so you don't lose the balance and fall back.