Part of the programme we will teach you is to maintain a natural lordosis , most of the time, especially when squatting or lunging. However its possible to attempt to over engage  your lordosis and crush joints together. the flexibility for squats and lunges comes through the hips, not by excessively arching your lumbar curve. The mantra is “find the problem, fix the problem”.  If when squatting you find ankle and hip flexibility issues, do not compensate in your back.