How does the human body response on exercise?

The reaction on the physical stress during spiroergometric examination is an immediate answer of great number of organs on the work of skeletal muscles. Their qualitative and quantitative values depend on the intensity and the workload duration. The human response can be divided into three parts - initial phase, steady state and recovery.

Initial Phase

The beginning of physical effort is connected with the large range of changes. This state can be called as unbalanced. The duration of this period and the extent of changes are depended on the intensity and the kind of stress and on the degree of individual adaptation at the same time. The maximum load causes permanent boom of all indices, which are very similar for different kinds of stress. However the difference exists in intensities of modulations. At the initial phase, the organism is not able to emit the energy by aerobic way, because the circulation and respiratory systems react more slowly and then the organism has to use a different way to obtain energy - anaerobic metabolism. Its intensity and effect depends on the evolution of oxygen uptake. Oxygen uptake increases after a few minutes up to the value given by the intensity of the exercise test, then it remains stable and after finishing the exercise test it starts to decrease continually. The amount of oxygen, which was missing at the beginning of work and which was needed to work in aerobic way, is called the oxygen deficit. The organism takes for same time after finishing the work a greater amount of oxygen than it would be normally needed at the rest. This amount is called the oxygen debt.

Figure: Change of Oxygen Uptake During Exercise [1]

Steady State

The steady state is reached as soon as the amount of oxygen covers completely the intensity of load. Aerobic metabolism is appeared under the conditions of the steady state and no lactate is produced. The heart rate and the breathing activity are kept at approximately same level. Absolute aerobic metabolism occurs mostly up to the intensity of aerobic threshold, when it is possible to cover the load without creation of lactate that means without the participation of anaerobic metabolism.


The phase of recovery coincides partially with the phase of oxygen debt when an organism received an increased amount of oxygen, higher than was pre-load quantity. Recovery is understood as a phase subsequent to physical stress and during which the effects of exercise are disappearing and the feeling of fatigue is declining. The length of recovery is directly dependent on the fatigue magnitude. The fatigue is a phase during which performance is gradually decreasing. During recovery are firstly eliminated products of metabolism such as lactate and the sources of energy are replenished.

Submaximal Testing

The above described mechanism stands up to the level of the anaerobic threshold (AT). It is necessary to exceed this level for the AT assessment. Therefore the AT is usually estimated with the help of submaximal testing which ends after subjective patientís distress during the incremental exercise test increased by a uniform amount each minute. A watt increment depends on the expected performance of the person.


[1] Placheta, Z.: Exercise diagnostic and activity prescription in the internal medicine. MU Brno: Brno, 1992 ©2007