Stress is defined as the sum-total of external influences (i.e. lifting and carrying loads, noise, volume of information) having an impact on the human organism which must cope with all these effects. Whereas stress is an objective quantity (i.e. load of 20 kg), strain means the response of the organism to all of the influences to which it is exposed and depends on the physical performance capacity of the person concerned. A strong man weighing 100 kg will perceive less strain when handling a load of 20 kg than a fragile woman weighing a mere 47 kg.