Complex sentence: However this is not the case, as it is the effect that is being expressed when using sieverts in J/kg. When using sieverts it is not the actual physical energy imparted by the incident radiation, but the calculated biological effect.
Split into simpler sentences: However this is not the case, as it is the biological effect that is being expressed when using sieverts. Sieverts do not represent the actual physical energy imparted by the incident radiation, but the calculated biological effect.