Tone is the amount of ‘tension’ inside a muscle when the muscle is at rest. Muscle tone is on a spectrum; it is possible to have normal muscle tone that is slightly on the low side or slightly on the high side. The tone of the muscles affects postural control and postural stability. This is important for helping you to stay upright and to stabilize you during movement.
However, if there is too much tension in the muscle at rest, we call this high tone (hypertonic). A hypertonic muscle is stiff and tensed even though it is not doing anything. It is difficult for hypertonic muscles to fully relax unless the child is asleep. As hypertonic muscles are usually held in a fixed position, the muscles need regular movement and stretches so that contractures (permanently shortened muscles) will not occur. High tone is common in children with spastic cerebral palsy.
Low tone (hypotonic) means there is not enough tension in the muscle when it is at rest. The muscle feels soft or floppy. A hypotonic muscle is slow to initiate a muscle contraction in response to a stimulus, and cannot maintain a contraction for as long as his typically developing peers. These are the "floppy" children who have difficulty maintaining any posture without external support. They may also lack endurance for gross and fine motor activities and may struggle with games that require coordinated, controlled movements. Older children with low muscle tone tire easily, have poor posture, tend to constantly lean against a support and find it difficult sitting or standing still. These children may have a difficult time at school as they are expending a lot of energy by constantly struggling to stay upright, instead of focusing on their lessons. Low tone is common in premature infants and children with some syndromes such as Down Syndrome and sometimes, in the early stages of cerebral palsy.
Muscle tone is controlled by the brain at an unconscious level and whether a child is born with either low, high, or normal tone is determined at birth. This is not something that can be changed permanently through exercise, and this should not be our goal during physiotherapy. High tone does not equate to higher strength. Instead what we usually see is that hypertonic muscles are actually very weak once the high tone is decreased by tone reducing methods, eg: botox injection, baclofen pills or pump or SDR (selective dorsal rhizotomy) surgery.
On the other hand, muscle strength occurs when you consciously (actively) contract your muscles to be able to pull, push, lift or move. Muscle strength is something that we can and should increase. Increasing the strength of muscles allows the body to compensate for the low tone. This is what we try to do during physiotherapy sessions.
Reproduced from http://kidzphysio.com/resources/difference-between-tone-and-strength/