People like cross training because it is intense, builds fitness quickly, and varies almost every day. Cross training is particularly popular with men and women in the military because it develops well-rounded fitness that prepares them for almost any physical challenge. Cross-training programs stress the body to the max. Exercise biochemistry studies have found that pushing the muscles close to failure results in the fastest rate of muscle protein synthesis and hypertrophy.
Unfortunately, failure training also increases the risk of severe muscle injury that can be debilitating or even life threatening. Overzealous cross trainers may develop rhabdomyolysis (rhabdo), which involves destruction of muscle tissue that results from the release of the muscle cell contents into the bloodstream. Toxic chemicals include myoglobin, creatine kinase, potassium, lactate dehydrogenase, uric acid, calcium, aspartate transaminase, alanine transaminase and phosphorus.
Typically, rhabdo turns the urine dark brown because of the presence of myoglobin. Symptoms might also include fainting, cardiac arrhythmias, compartment syndromes (inflamed muscles trapped by bone or soft tissue), muscle pain and weakness, nausea and vomiting. The severity and risk of rhabdo increases with dehydration, eccentric exercise (negatives or lengthening contractions), trauma, and even medically prescribed drugs such as statins.
The incidence of rhabdo has increased alarmingly with the popularity of high-intensity training programs. Approximately three percent of people involved in physical training programs for the military, police and fire departments experience rhabdo. Physicians across the country have reported an increased incidence in ordinary people performing extreme physical training programs in health clubs. The exact percentage is unknown, but experts believe that the incidence is under reported.
Rhabdo and Cross Training
Cross training programs typically involve high-rep, high-intensity exercises such as kettlebell swings and snatches, thrusters, squats, sit-ups, sprints and pull-ups. While these exercises build whole-body fitness rapidly, they can cause muscle cell destruction if pushed too far. There is sometimes a fine line between building muscle fitness and muscle destruction.
Recent scientific studies on muscle hypertrophy found that muscle size increases best when muscles are pushed to failure or close to it. Failure training typically involves exercising using relatively light weights for as many reps as possible. This technique maxes out recruitment of fast- and slow-twitch muscle fibers and is an excellent way to promote muscle protein synthesis. There are pluses and minuses to this training technique. The few studies that examined failure training showed that it increased muscle mass and strength better than other training techniques. However, it also delays recovery. In strength sports requiring movement skills, failure training could interfere with sports practice. Also, excessive training to failure, such as used in "boot camp" and cross-training programs, can increase the risk of rhabdo.
Most people have experienced delayed onset muscle soreness (DOMS). DOMS is caused by injuries to the muscle cells that release calcium into the cell contents. Calcium triggers the production of chemicals called proteases that cause further breakdown in vital cell structures. While DOMS is painful and may temporarily decrease performance, the problem is usually not serious. Also, the muscle repair process associated with muscle soreness may be important in promoting muscle hypertrophy and increasing strength.
Rhabdo caused by excessive exercise is basically delayed onset muscle soreness that goes too far. Like DOMS, rhabdo is linked to calcium release that causes cell inflammation and destruction of vital muscle cell membranes. However, rhabdo is more severe than DOMS and results in the release of toxic chemicals into the bloodstream. Cross trainers must perform a delicate balancing act that pushes the muscles hard enough to cause some damage but not so hard as to cause severe muscle damage and rhabdomyolysis.
Cholesterol-lowering drugs called statins also increase the risk of rhabdomyolysis. Increasingly, physicians are prescribing statins to young adults with increased risk of coronary artery disease. Risk factors include obesity, high blood pressure, insulin resistance and high blood sugar, abnormal blood fats and inflammation. Some researchers feel that statins should be widely prescribed in young adults to prevent heart attacks, Alzheimer’s disease, and abnormal blood fats such as high cholesterol and elevated LDL. Statins also cause muscle achiness and decreased physical performance. They are linked to muscle fatigue in about 25 percent of casual exercisers and 75 percent of intensely training athletes. Statins could pose a serious risk for muscle damage in cross trainers. People must balance the benefits of reducing the risk of coronary artery disease with the negative effects of statins on physical performance and muscle health.
Preventing Rhabdomyolysis During Cross Training
Some cross trainers consider rhabdo a badge of honor. This is a mistake. Exercise-related muscle damage can cause decreased performance, muscle pain, kidney failure and even death. However, you can train intensely and safely if you follow a few basic principles:
- Get in shape gradually. Muscles produce protective proteins that strengthen muscles after intense exercise. If you are a beginner, don’t do a cross-training program designed for a well-trained athlete. If you take a break from training, don’t start where you left off. Rather, increase the intensity of exercise gradually for two to three weeks. Ex-athletes are particularly susceptible to rhabdo because they remember how to train hard but no longer have the fitness.
- Exercise within your capacity. Physical training is an adaptive process that is highly individual. Genetic studies show that there are responders and nonresponders to exercise. If you are a hard gainer, don’t overcompensate by doing excessive exercise.
- Don’t overdo eccentric exercise (lengthening contractions or negatives). Rhabdo has been reported in people doing high-repetition squats, kettlebell swings and snatches, thrusters and downhill running.
- Don’t train hard when you are sick. Illnesses accompanied by fever can affect muscle function and increase the susceptibility to rhabdo. Viruses, such as influenza A and B, Epstein-Barr, herpes simplex and human immunodeficiency virus (HIV) are linked to an increased risk of rhabdo.
- Be aware of the warning signs of rhabdomyolysis. See your physician immediately if you develop dark, brown-colored urine within two or three days following an intense workout. Rhabdo is an inflammatory process that may get worse 36 to 48 hours after a workout. Other symptoms include muscle weakness, muscle tenderness, extreme fatigue, joint pain, seizures, inability to recover, nausea, vomiting and faintness. Rhabdo is often misdiagnosed because common blood tests such as myoglobin and creatine kinase are insensitive markers of the problem.
- Beware of assisted spotting during failure training. While this technique is effective for pushing muscles to the max, it can result in muscle destruction in unfit or susceptible people. Avoid doing drop sets (multiple sets performed to exhaustion, decreasing the weight after each set) until you are well trained.
- Stay hydrated. In general, let thirst be your guide in determining fluid intake. But make sure you take in enough fluid to satisfy your needs. Dark urine color may be a sign of dehydration. Be aware that vitamin supplements can make your urine darker.
- Hyperthermia (high body temperature) increases the risk of rhabdomyolysis. Take care not to exercise excessively in the heat. Physical fitness is the best protection against heat illnesses. Avoid sitting in hot tubs after performing monster workouts. Recent studies have found that cold water baths help decrease inflammation after intense muscular exercise.
- Balance the risks and benefits of statin therapy to reduce cholesterol and prevent heart disease. Statin use in intensely training athletes is highly controversial. Learn as much as you can about this topic and have a frank discussion with your physician. Some experts recommend suspending statin therapy for five to seven days before competition.
Most people don’t exercise hard enough. Fifty percent of Americans don’t meet the minimum recommendation of 150 minutes per week of moderate-intensity exercise. However, cross trainers are a competitive, hard-driving group of people. They are more likely to overtrain in an effort to reach top-level fitness. They have an increased risk of developing exercise-induced rhabdomyolysis. The take-home message is to train intensely, but not too intensely.
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