Blood Starvation of Muscles During Training

muscle fiber fasicle

Blood flow restriction to muscles during training was shown by a recent study to induce changes in the muscle that increased contractile function. These changes were observed at the cellular and biochemical level.


An exciting field of research right now is how the muscles act when blood flow is constricted. A recent study showed that constricting blood flow during training increased muscle fiber cross sectional area, muscle stem cells and nuclei in the muscle (myonuclei).

The study (Jakob Nielsen, et al. 2012.  Proliferation of myogenic stem cells in human skeletal muscle in response to low-load resistance training with blood flow restriction) assigned twenty healthy males to perform 23 knee extension training bouts for a period of 19 days. Ten subjects performed the training with a pneumatic cuff placed on their thigh to limit blood flow (blood flow restriction or BFR). The other ten subjects served as a control and had no blood flow restriction. Muscle biopsies were taken pre-training, 8 days into the training intervention, 3 days post-training intervention and 10 days post-training intervention.

Interestingly, the subjects who had their blood flow restricted retained an increase in strength 5 days and 10 days post training intervention. The control subjects’ strength returned to pre-intervention levels 10 days post-training intervention. The cause of this sustained strength increase in the experimental group can be explained at the cellular and biochemical level.

Subjects who had their blood flow restricted saw increases in muscle stem cells, muscle nuclei, and muscle fiber cross sectional area. The differences were measured by muscle type as well.  Type I fibers are slow twitch fibers, responsible for aerobic work. Type II fibers are fast twitch and provide anaerobic work. Both mucle fiber types saw a large increase in Pax7+ expressing stem cells in subjects who had blood flow constricted. As the figure below shows, both muscle fiber types saw an increase in myonuclei when the subject had blood flow to the muscle constricted (blood flow restriction or BFR). The BFR change in type II muscle is surprising given the low intensity (normally aerobic) exercise. No change in either muscle fiber type was seen post-training in the control group (CON).

The muscle fiber cross-sectional area increased in both groups of subjects during training. However, the control group lost virtually all gains post-training. The blood flow restriction group maintained gains in muscle fiber cross sectional area 3 and 10 days post training. The authors suggest that hypoxia-induced protein synthesis is responsible for the gains seen in muscle fiber cross-sectional area in the blood flow restricted muscles.

In conclusion, blood flow restriction during training appeared to strengthen muscle function even after the cessation of the training program. The muscle achieved an increase in contractile power through increases in muscle fiber cross-sectional area, muscle stem cells, and myonuclei.  The discussed results have clinical significance: blood flow restriction may help patients regain lost or damaged muscle.

However, blood flow restriction likely does not extend beyond potential clinical applications to elite training programs.  Both groups followed the same training sequence. It would be reasonable to believe that training performance would be hurt by blood flow restriction. Thus, for a healthy, elite athlete doing high-intensity training, blood flow restriction would hamper their ability in a workout.

Heat, the Brain and Fatigue

sun hot heat sweat 

Heat limits athletic performance. The way heat causes fatigue may be through an elevated brain temperature.



Our bodies do not perform as well in hot conditions. Hyperthermia is when the body gets overheated resulting in a decrease in maximal power output. Most of us have experienced the fatigue that occurs with heat while exercising or during labor. Personal experience tells us that heat creates fatigue, but what is the physiologically basis of this heat-induced fatigue?

Before looking at how heat affects performance it is important to understand fatigue. There is much debate among today’s exercise physiologists about what actually limits performance during maximal-effort exercise. It is a muscles versus brain dissension. Do the muscles tire, signaling fatigue to the brain or does the brain, in an effort to avoid injuring muscle tissue, signal fatigue to the muscles? The idea that the brain is actually responsible for limiting performance was first introduced in the late 19th century, but has not yet been proven.

A hot environment makes it harder for the body to regulate its body temperature during exercise for several reasons. Blood cools off muscle tissue by moving into the body’s core and out to the skin. A hot environment means that the skin is unable to dissipate heat easily due to a reduced temperature gradient. The elevated temperature of the skin also lowers the temperature gradient between the body’s core and skin. During exercise in a hot environment, blood is simultaneously needed to deliver oxygen to the muscles and to thermoregulate by going to the skin. To make matters worse, blood pressure is reduced because water is being lost as sweat. This strain on available blood is why dehydration is so detrimental to athletic performance in hot environments.

One study found that regardless of the temperature of the exterior environment fatigue always sets in at the same core body temperature [Walters, et al. (2000). Exercise in the heat is limited by a critical internal temperature.]. The authors reasoned that a warm environment simply means that the “critical” core body temperature is reached sooner. However, this critical core body temperature theory has been challenged recently by studies showing ways of altering the critical core body temperature. Dopamine and caffeine were both shown to increase the core body temperature that fatigue sets in. Dehydration, on the other hand, lowered the core body temperature at which fatigue set in. Therefore, not only does being dehydrated mean that your body has a harder time regulating its body temperature, but the body temperature at which fatigue comes on is lower.

Force exerted as a function of time and hyperthermia condition. Four electrical stimulations (EL) were done demonstrating that the muscle was capable of greater exertion from the EL than brain stimulation. Hyperthermia had less effect on muscle contraction during electrical stimulation than brain stimulation.

The brain’s ability to regulate its temperature is stressed during exercise. Cerebral metabolism increases during exercise. Yet, the brain must deal with reduced cerebral blood flow because blood is being diverted to active muscles and thermoregulating skin. It is hard to determine if the core body temperature or brain temperature is responsible for fatigue. Because the brain gets arterial blood from the body core their temperatures are closely linked. Thus, a hot body core results in a hot brain. The brain is typically a fifth of a degree Celsius above the core body temperature. One recent study used experimental techniques to selectively heat the brain during exercise (Lars Nybo, 2012. Brain temperature and exercise performance). The results suggest that the brain’s temperature has a significant impact on performance. However, other studies have concluded that the skin’s temperature sensors are responsible for hyperthermia fatigue [Sawka et al. (2012). High skin temperature and hypohydration impair aerobic performance].

In conclusion, it appears that hyperthermia causes fatigue by elevating the brain’s temperature. Much debate still remains regarding the source of fatigue and the role that hyperthermia plays on fatigue. Understanding the way that heat decreases performance will provide avenues for increasing athletic capability in warm environments.

Rebuilding Muscle Protein

myosin structureMuscle protein synthesis is activated through exercise and nutrition. This myosin molecule (right) is one of many muscle proteins that are generated during muscle protein synthesis following exercise or an amino acid rich meal.


For a competitive athlete, one of the primary goals of working out is to stimulate muscle protein synthesis.  Muscle protein synthesis drives muscle hypertrophy, an increase in muscle mass.  There are two ways to drive muscle protein synthesis: nutrition and exercise.  Foods with essential amino acids stimulate muscle protein synthesis. Muscle protein synthesis is especially important after resistance training like lifting weights, but is also at play following endurance activities such as swimming or cycling.

If essential amino acid intake stimulates muscle growth why can’t someone build muscle mass by eating lots of protein? The reason is the “muscle full” response.  According to a 2012 review by PJ Atherton and K Smith entitled Muscle Protein synthesis in response to nutrition and exercise (Issue 590 of The Journal of Physiology) the “muscle full” response halts amino acid uptake. Muscles will take up amino acids for about 90 minutes before the muscle full point is reached.  Following resistance training, the muscle will take up amino acids for an extended period of time. Interestingly, this exercise-induced extension of the muscle full response occurs up to 24 hours post-exercise bout.

Muscles continue to take up essential amino acids for an extended duration 24 hours post exercise.

Following exercise the body uses the amino acid equivalent of 20 grams of protein. In addition, the way in which the body stores amino acids for muscle protein synthesis suggests that a greater frequency of small protein meals trumps one large meal. While amino acids trigger muscle protein synthesis, insulin decreases muscle protein breakdown. Insulin controls sugar levels in the blood by lowering blood sugar levels following a meal. However, insulin also rises following a meal that is carbohydrate free in order to halt catabolic muscle protein breakdown.

A trained athlete will have a specific muscle protein synthesis response. Due to increased efficiency, the trained athlete will spend less time doing muscle protein synthesis following exercise. This specificity means that an endurance athlete will build mitochondrial protein (mitochondria power aerobic work), but not myofibrillar protein. Resistance trained athletes will have post-exercise myofibrillar synthesis, but not mitochondrial protein synthesis.  An elegant study demonstrated this by having athletes exercise one leg on a cycle bike and another leg on a resistance machine (Wilkinson et al 2008). A person who rarely exercises will have a less specific and efficient muscle protein synthesis response following a workout.

In conclusion, nutrition and exercise have an overlapping role in regulating muscle protein synthesis. Determining the optimal conditions of muscle protein synthesis would aid athletes interested in bettering their performance.

The Physiology of Icing Sore Muscles

meb marathon new york


Meb Keflezighi (left, winning the 2009 NYC marathon) credits much of his success to icing.



About a year ago I met Meb Keflezighi, one of the greatest American marathon runners of all-time, while training at Mammoth Mountain in California. Since then the 37 year-old stud has had a very successful season culminating in a fourth place finish at the 2012 London Olympics. During our meeting he stressed the importance of icing on his success. Therefore, I was not too surprised that Meb emphasized his devotion to icing during media interviews after winning the 2012 American Olympic marathon trials. Meb is unquestionably one of the world’s most elite marathon runners. However, the question remains: What part has icing played on Meb’s running career?

Although studies looking at the effects of icing, or cryotherapy, have had somewhat conflicting results, most studies have found icing following exercise-induced muscle damage to be beneficial. The extent of muscle damage peaks between 24 and 72 hours following strenuous exercise. Exercise-induced muscle damage includes sarcolemma disruption, fragmentation of the sarcoplasmic reticulum, lesions of the plasma membrane cytoskeletal damage and swollen mitochondria. Outside the muscle fiber there may be swelling due to an increase in blood flow and capillary permeability.

One study looked at the multi-day effects of icing on exercise-induced muscle damage (Effects of cold water immersion on the symptoms of exercise-induced muscle damage, 1999, Roger Eston and Daniel Peters). The study used 15 female subjects and endurance exercised their biceps. The cryotherapy group submerged their exercised arm into a tub of 15 degrees Celsius  water for 15 minutes. This treatment was administered immediately after the bout of exercise and every 12 hours thereafter for 3 days.

The study results show that creatine kinase activity, a predictor of muscle damage, was lower in the cryotherapy treated group two and three days after the bout of exercise. The graph below shows these results.

Screen Shot 2012-08-19 at 4.36.27 PM

Eston and Peters also showed that the arm circumference and tenderness were not significantly affected. However, arm strength returned to baseline much faster in the cryotherapy group. This is of particular interest to athletes who often are expected to complete consecutive workouts in a 72 hour timeframe.  The difference was significant: after 72 hours the control group had a mean isometric strength that was 86% of baseline while the cryotherapy group had a mean isometric strength that was 111% of baseline.

A more recent study on the subject of icing measured blood flow, temperature and muscle endurance in cryotherapy treated and control groups (Changes in Blood Flow, Temperature and Muscle Endurance in Association with Cryotherapy, 2009, Masahiro Utsunomiya, et al.). In this Japanese study three groups were established: resting group (10 minute rest), 2-minute cooling group (2 minute icing and 8 minutes of rest) and 10-minute cooling group (10 minutes of icing).  Endurance was significantly boosted by icing. After ten minutes of rest the resting group performed at 59.2% of the initial test, the 2-minute cooling group 73.1% of initial test and the 10-minute cooling group 80.7% of the initial test. This suggests that the effects of icing are immediate.  Decreases in deep part temperature and tissue circulating volume were also observed as duration of icing increased.

The authors suggested that the cooling decreased oxygen consumption and cellular metabolism. This would potentially increase muscle endurance.  However,  an EMG signal processed with Fast Fourier Transformation saw no significant differences between the groups during the second bout of training. The authors hypothesized that the lack of significance means differences in endurance could have been the result of lowering myogenic pain instead of an increase in physiological fatigue.

The Running Mechanics of Elite African and Caucasian Marathoners

Hall Ryan olympics

Ryan Hall, one of the greatest marathoners not of African descent. Although his form contributed to his running efficiency, he was forced into retirement from injuries.


The mechanics of the perfect running form we should all strive for…


An interesting video comparing the running mechanics of some of the fastest African and Caucasian marathon runners including Ryan Hall and Meb. Meb is still chasing medals in the 2016 Rio Olympics, while Ryan Hall retired after injuries derailed his career. This video offers suggestions for enhancing performance and preventing injuries. Brought to  you by Somax Performance Institute, a renowned sports science center just north of San Francisco. Enjoy!

Glycogen Starvation in Muscle Training

glycogenGlycogen efficiently stores glucose in a branched, dense polymer. A study released in 2004 suggests that glycogen starvation during training increases endurance performance.

Glycogen is polymerized glucose. For athletes, glycogen has many advantages. When glycogen is broken down into pyruvate during glycolysis it results in a net gain of 3 ATPs. ATP is our body’s and muscle’s high-energy delivering molecule. When glucose is broken down during glycolysis it produces just 2 ATP. Thus, glycogen produces 50% more ATP during glycolysis than glucose. When the cell is in hypoxia (oxygen depletion) it is unable to break down the glycolysis product, pyruvate, further. Thus, for anaerobic exercise, glycogen breakdown results in a considerable energy benefit. In addition, as the image above shows, glycogen is branched every ten glucose monomers. This allows more glucose molecules to be available for glycolysis (only glucose molecules at the end of a chain can be cleaved). Over the course of animal evolution, glycogen has developed into the primary energy-storage molecule because of its denseness and efficient energy-release.

Glycogen has long been known to be beneficial to athletes; hence carbohydrate loading (carbo loading’s affect on performance is debatable, but that is another story). Is glycogen beneficial during training?  That is the question an elegant Danish study sought to answer. The study found that carbohydrate depletion during training was beneficial to performance (Skeletal Muscle Adaptation: training twice every second day vs training once daily; 2004; Anne K. Hansen, et al.)

The study took 7 healthy, untrained men and put them on a strict training schedule for ten weeks.  The training consisted of leg extensions. Each participant worked out both legs for an hour, wait two hours under a fast, and workout one of the legs (low-glycogen protocol) for an hour. The next day, the participant would workout the other leg (high-glycogen protocol) for an hour. On this two-day sequence both legs got two hours of work, but one at lower levels of glycogen than the other. This is because following the first hour bout of exercise, glycogen levels in the muscle drop. The two-day sequence was repeated for ten weeks.  The experimental sequence can be seen in the diagram below.

Schematic overview showing the design of the study.

In response to 10 weeks of training, maximum power output increased significantly, being the same in the two legs. The endurance at 90% of this new maximum power output was markedly increased for both legs, but time until exhaustion was twice as long for low-glucose protocol trained legs compared with high-glucose protocol trained legs. In accordance, the actual work performed by low-glucose protocol trained legs was also markedly larger compared with high-glucose protocol trained legs. The results can be seen in the table below.

Maximal power output and time until exhaustion at 90% of maximal power output before and after 10 weeks of training and total work before and after 10 weeks of training.

Muscle glycogen levels were raised significantly in low-glycogen protocol trained legs at the conclusion of 10 weeks of training. The authors of the study speculated that this may have been the result of a change in GS enzyme, a regulator of glycogen production. Mitochondria enzymes CS and HAD were both significantly higher in low-glycogen protocol trained legs.

The results of this study seem to support this hypothesis regarding glycogen: train low, perform high. However, these results must be treated with caution when applied to athletes. Other factors could be at play; training twice every other day compared to once daily may affect other pathways besides glycogen. In addition, glycogen starvation would potentially limit the amount of training one could conceivably do.

In summary, this study suggests, but does not prove, that glycogen starvation during training may increase endurance.

Saving Time with High Intensity Training

high speed cyclist

High-intensity interval training has been shown in recent studies to boost endurance performance and health. High-intensity interval training offers benefits seen in continuous endurance training with less time commitment.


The time commitment required for exercise on a daily basis is often cited as the reason people don’t exercise. High-intensity interval training may be a time-saving tool for both the recreational exerciser trying to stay healthy and the elite endurance athlete trying to out-train the competition.

Studies on the physiological effects of high-intensity training have been produced since the 1990’s. A study was published in 1997 on the effect of high intensity interval training on cyclists. Cyclists who replaced 2% of their weekly endurance training mileage with short (6-9 minutes) high-intensity (80% max) intervals were found to show significant improvements in a 40km time trial. In 1999, a study looked at the affects of varying the high-intensity time interval (Effects of different interval-training programs on cycling time trial performance, 1999, NK Stepto, et al.). The results can be seen in the figure below.

The effect of varying the intensity of interval training on changes in 40 km time-trial performance. Well-trained male cyclists were randomly assigned to one of five different doses of high-intensity interval training (HIT): 12 × 30 s at 175% of peak sustained power output (PPO), 12 × 1 min s at 100% PPO, 12 × 2 min at 90% PPO, 8 × 4 min at 85% PPO, or 4 × 8 min at 80% PPO. Cyclists completed six HIT sessions over a 3 week period in addition to their habitual aerobic base training.

For elite athletes, the success garnered with intensity polarization cannot be limited to cyclists. In 2009, a study found that rowers who dedicated just 5% of their training to more intense intervals had a higher chance of going on to compete on an international stage. The study looked at rowers over a three-year time frame (Training methods and intensity distribution of young world-class rowers, 2009, A Guellich, S Seller, E Emrich).

Most people, however, are not interested in exercise as a means of improving peak performance.  For many, exercise is a prescription for staying healthy. A study published in 2012 found that through high-intensity interval training patients could achieve the same physiological benefits of continuous endurance training in a third of the time (Physiological adaptations to low volume, high intensity interval training in health and disease, 2012, Martin J. Gibala,  et al.). The study found that participants who did 10 one-minute bouts at 90% maximal heart rate with a minute of recovery (10 minutes of work, 20 minutes total) showed similar skeletal muscle metabolic adaptations and cardiovascular adaptations to a control group doing 60 minutes of continuous exercise. This suggests that this high-intensity interval training may alleviate diseases just like endurance training. However, no research has been done yet to set up a link between disease risk and high-intensity interval training.

In summary, performance and health can both be boosted by high-intensity interval training. The benefits include a more enjoyable workout (most people prefer interval training to continuous endurance training) in less time and improvement in functional performance.

Fighting Belly Cramps

triathletes running next to lakeBelly cramps are caused by a variety of gastrointestinal tract issues. However, they can be prevented by staying hydrated, eating a diet high in fiber, avoiding potential allergens and clearing the colon before intense physical activity.




Every athlete has suffered through belly cramps. Often they appear out of the blue. However, they can be fought with the right diet, hydration and empty colon. The intense abdominal pain is caused by disturbances in the gastrointestinal tract. The symptoms can range from a minor disturbance during or following exercise to nausea, vomiting, diarrhea and severe abdominal pain.

A recent study looked at 12 endurance athletes, ranging from recreational to elite, for causes of gastrointestinal symptoms. All 12 athletes were found to suffer from gastrointestinal ischaemia during periods of maximal exercise (Abdominal symptoms during physical exercise and the role of gastrointestinal ischaemia: a study in 12 symptomatic athletes; 2011; Steege, et al.). Gastrointestinal ischaemia is the depletion of blood flowing to the colon. When not enough blood reaches the colon it hurts due to the lack of oxygen. In hot or humid environments, gastrointestinal ischaemia is especially acute because more blood is diverted to the skin for thermoregulation. Two other causes of gastrointestinal complaints during exercise are gastric emptying delay and food-dependent exercise-induced anaphylaxis (FDEIA). Gastric emptying delay is when food remains in the stomach for an extended amount of pain. FDEIA is any allergen reaction in the gut. Exercise facilitates allergen absorption in the gastrointestinal tract.

How are these gastrointestinal complaints prevented? A Brazilian review on the subject provides some answers (Food-dependent, exercise-induced gastrointestinal distress; 2011, EP Oliveiera and RC Burini). FDEIA is caused by consuming allergen-specific foods within a few hours preceding exercise. Foods found to be associated with FDEIA include cereals, seafood, peanuts, tree nuts, eggs, milk and vegetables. Gastric emptying delay can be fought by staying hydrated and avoiding replacement fluid with high levels of glucose and hypertonic solutions in general. A fructose-glucose mix has been shown to replenish muscle energy with increased gastrointestinal carbohydrate oxidation. Staying hydrated, but not overly so, is the best way to fight gastrointestinal complaints with the added benefit that it assists with thermoregulation.

Diets high in fiber, like these apples, prevent stomach cramps.

The best way to fight gastrointestinal ischemia is by clearing the colon. Exercise induces powerful contractions in the intestines that drive food forward along the gastrointestinal tract. This increases the amount of blood desired by the colon. Fiber holds moisture in the colon. Foods high in fiber keep stool soft allowing it to clear out easier. To ensure your diet is high in fiber, eat a diet with lots of fruits and vegetables. Avoid white-flour foods which are low in fiber and bulky. Passing stool at the same time time on a daily basis can condition the processes driving stool out of the colon.

In summary, in order to prevent abdominal cramping: stay hydrated, eat fiber, avoid potential allergens and clear your colon before an intense workout or race.