Strength training has a given place in training for sports, in rehabilitation after injuries and illnesses of various kinds, and in the training that takes place as a preventive measure to counter the emergence of various ailments.
Increasingly, resistance exercise is also included as part of the treatment to counteract the negative effects of chronic disease and injury. However, it is not always possible to train with the heavy loads that conventional weight training requires, and sometimes there are also reasons not to do so, for example with regard to joints and ligaments.
Strength training with restriction of blood flow
Over the past 10-12 years, a new type of strength training has been introduced, ischemic strength training or occlusion training. In the most common form of ischemic resistance exercise, a pressure cuff is applied around the leg or arm to be trained in order to reduce the blood flow to the working muscles. The method was invented by a Japanese physiotherapist, who called it "Kaatsu training". Kaatsu is Japanese and roughly means "applied pressure." In this type of exercise, the muscles are working with inadequate blood flow (ischemia), which, in turn, among other things leads to a temporary lack of oxygen (hypoxia) in the affected tissues.
Brief episodes of hypoxia occur relatively frequently in the muscles during normal exercise, especially during intense weight training, but provided that the hypoxia / ischemia does not last for too long, physiological adaptations occur so that the muscles can withstand this kind of stress better.
Good training effects despite low loads
In conventional heavy resistance exercise, the loads are typically about 70-85% of 1 RM or even higher (1RM = one repetition maximum, the maximum weight that can be lifted only once).
In occlusion training, significantly lower weights are often used (~ 20-50% of 1 RM), but despite the low loads, resistance exercise with restriction of blood flow induces increases in both strength and muscle volume.Good training effects have been demonstrated in both healthy untrained individuals and trained athletes, as well as in the elderly and patients rehabilitating after injury.
The mechanisms behind the positive training effects are of great interest
Since occlusion training, with its often low loads and many repetitions, seems to conflict with the basic principles of strength training, it is likely that more knowledge about the mechanisms behind this type of exercise can provide greater insight into the physiology behind muscle growth. This in turn could lead to improved therapeutic treatments aimed at maintaining or increasing muscle mass and muscle function in different groups of individuals.
It is therefore of great interest both from a practical standpoint and from a basic research point of view to try to clarify why occlusion training works.
Delayed onset muscle soreness with occlusion training!
The first study in the thesis examined the effects of occlusion with a pressure cuff on the endurance in the knee extension exercise in a conventional "Leg Extension" machine with weight stack. As expected, occlusion resulted in a reduced muscle endurance during the exercise.
One of the incidental findings of this study was that the subjects reported a noticeable muscle soreness 24-48 hours after occlusion training at such low loads as 20% of 1RM. That heavy resistance exercise and eccentric training can result in soreness is well known, but before this study there was no report in the literature that occlusion training can also induce muscle soreness.
High muscle activity with occlusion training.
Study number 2 investigated the effects of partial occlusion with a pressure cuff on muscle activity in the quadriceps during knee extensions with low weight (30% of 1RM). Muscle activity (measured by electromyography, EMG) increased gradually with increasing severity of fatigue in the working muscles, to eventually reach levels that were very close to those observed in heavy weight training.
Muscle activity increased not only during weight lifting (the concentric phase) but also during the braking (eccentric) phase when the weight was lowered back to the starting position. That EMG increases during the concentric phase during occlusion training was known previously, but that it does also during the eccentric phase was not reported before.
Signs of increased permeability of the muscle cell membrane with occlusion training.
The third study examined the effects of an acute training session with occlusion training on muscle function and muscle fiber morphology. The protocol was knee extensions at 30% of 1RM with multiple series to failure, and partial restriction of blood flow. The results showed that the subjects needed more than 48 hours of restitution after the training session for muscle strength to get their strength back to baseline levels, indicating that muscle function was temporarily impaired.
At the muscle fiber level, there were signs of an increased permeability of the muscle fiber membrane (sarcolemma). Tetranectin, a protein which is present in human plasma, was seen inside an increased number of the muscle fibers after the exercise bout, indicating that the membranes had become more permeable. This can be interpreted as the sarcolemma becoming temporarily injured, but an increase in membrane permeability and increased degradation of membrane components could also be some of the stimuli that is transduced into signals for muscle fiber growth.
Signs of increased permeability of muscle fiber sarcolemma, such increased muscle proteins in the blood, are common in heavy strength training, especially in untrained subjects or when training resumes after a break. This study is the first to show signs of increased membrane permeability with occlusion training.
Prolonged cell signaling and activation of satellite cells with occlusion training.
In study 4, the focus was on effects of an acute training session on the muscle cell's internal signaling, and the activation of the muscle's own stem cells, called satellite cells.The training protocol was the same as in the third study. The results showed that phosphorylation of the enzyme p70S6 kinase (p70S6K), a marker of protein synthesis and muscle growth, was already increased at one hour after the exercise bout and that this increase was maintained at 24 hours post-exercise. This has been observed after heavy resistance exercise and eccentric training, but this study is the first to show that this can be achieved also with occlusion training. This long duration suggests that occlusion training, like heavy strength training, may cause increases in muscle protein synthesis that lasts at least 24 hours.
The number of satellite cells around the muscle fibers increased after the exercise. This has previously been observed after heavy strength training and eccentric exercise, but this study is the first to show that satellite cells can increase in numbers already after a single bout of occlusion training. An increased number of satellite cells is probably favorable for muscle growth and may eventually contribute to more myonuclei in muscle fibers.
Implications for further research and practical implications of the work
In summary, the studies in this thesis indicate that occlusion training, despite low loads, has several similarities with heavy resistance exercise. Both modes of training can result in muscle soreness, high muscle activity, signs of muscle fiber damage, long-lasting increases in cell signaling and an increased number of satellite cells. It can be speculated whether a temporarily increased membrane permeability of the muscle fibers could contribute to soreness as well as effects on cell signaling associated with muscle growth and activation of satellite cells.
For therapists and trainers who are considering using this mode of training, it is important to know that occlusion training can induce muscle fiber damage in individuals who have not tried this type of training earlier.
There are also case reports and observations that a first-time bout of occlusion training can cause massive leakage of muscle proteins into the blood, indicating severe muscle damage. It is therefore recommended that the training starts cautiously and that effort and training volume are increased gradually to reduce the risk of excessive muscle fiber damage.
Programme Friday November 11th, 2011
10.15 - 11.00 Trial lecture : "Satellite cells, are they necessary for muscle growth in adult human muscle or not?"
13.00 - 16.00 Doctoral defense
||Mathias Wernbom is from Gothenburg and obtained his physiotherapy degree in the same city. He has also studied physiology in Gothenburg and sports physiology in Stockholm, Umeå and Odense.He has a master's degree in sports medicine from the University of Umeå and has in addition to work as a physiotherapist also worked for many years as a strength training instructor and personal trainer.