Chapter 15: middle adulthood physical and cognitive development. Some theorists view middle age as a time of peak performance, whereas others portray it as a time of crisis or decline. L01: describe trends in physical development in middle adulthood. Physical development: interindividual variability no two people age in the same way or at the same rate; physiological aging is defined by changes in the body"s integumenary system, may well be unavoidable. Skin and hair: production of melanin decreases pigment responsible for hair colour, wrinkling, grey hair, skins loses elasticity because it"s producing fewer proteins, fewer keratinocytes produced skin dyer and more brittle. Sensory functioning: vision presbyopia loss of elasticity in the lens; makes it harder to focus on, accommodate nearby objects/fine print. Lung capacity down the process: lung tissue stiffens with age, limiting capacity to expand; exercise can help slow.