Muscle soreness and fatigue are two common symptoms associated with beginning a new exercise program. The sudden ramp up in physical activity places unexpected stress on our muscles and joints, which in turn leads to pronounced soreness. Additionally, our bodies’ cardiovascular response to heightened physical activity is sluggish at the onset of an exercise routine because the body’s systems weaken when not regularly used.
As an exercise program progresses, the body adapts to overcome both symptoms. Our muscles and joints strengthen with greater activity and become conditioned to accept the increased demand for motion, which reduces soreness. Our lungs, heart, blood vessels and other elements of our circulatory system also adapt to the increased demands for energy associated with exercise by improving the efficiency of oxygen and glucose transfer to cells in the body calling for more energy.
But it can be tough to get excited to exercise when you are fatigued and sore before you even start a workout.
You can reduce the likelihood of soreness by starting a new program with low-impact forms of exercise such as walking and stretching. You can also limit the amount of time you work out to 20 minutes or so at the beginning. Then, as you build stamina, you can increase the intensity and duration of your workouts.
But even these measures won’t completely eliminate aches and fatigue early in a new physical activity routine. So, in addition to starting with a low-impact, low-intensity program for a short duration, are there other steps you can take to reduce fatigue?
According to a recently published research study, one such step might be adding 1,200 mg of the dietary supplement N-acetyl cysteine (NAC) to your daily routine.
Why NAC and What Does it Have to do With Fatigue?
NAC is an amino acid that, when ingested in humans, is converted by the body into the powerful antioxidant glutathione. Glutathione has been shown in previous studies to be recruited in the body to offset free radical oxygen molecules that are by-products of burning energy.
The creation of excess free radicals is known as oxidative stress, and oxidative stress contributes to the inflammation of muscles and other tissues. Researchers have found that glutathione levels are depressed during exercise and that supplementing NAC has been shown to delay muscle fatigue in certain populations (such as those with respiratory conditions).
The goal of the current study was to see if supplementing NAC would help untrained, sedentary study subjects maintain glutathione levels post-exercise, i.e., reduce the impact of oxidative stress and inflammation, and then to see if the boost in glutathione levels would appreciably affect exercise performance and fatigue.
Putting NAC to the Test
To test their hypothesis, researchers enrolled 29 sedentary, physically inactive men with an average age of 20 into the study. At the outset of the study, the men were divided into two groups. Sixteen of the men received 1,200 mg of NAC each day over the course of the seven-day study period (600 mg with their morning meal and 600 mg with their evening meal). The remaining 13 men were labeled as the control group and did not receive NAC.
Participants in both groups had blood samples drawn to look for glutathione levels and known markers of oxidative stress and inflammation. Then they participated in a fatigue endurance test and a graded exercise test. Graded in this context means each workout began at a low intensity and, at defined intervals during the workout, the intensity was increased until subjects achieved heart rates equivalent to 85 percent of their maximum heart rate.
Maximum heart rate is typically defined as 220 minus your age. So if you are 50 years old, your maximum heart rate is pegged at 170 beats per minute, and 85 percent of your maximum heart rate is approximately 145 beats per minute.
Twenty minutes after the initial exercise tests, blood was drawn again to provide the researchers with baseline pre- and post-exercise levels of the various markers.
Then, over the next seven days, the NAC group received 1,200 mg daily of NAC while the control group received no supplementation. At the end of the seven-day period, the researchers invited the participants back to provide new blood samples in advance of follow-up exercise tests, and blood was also drawn 20 minutes after the second exercise test.
Researchers compared the pre- and post-exercise levels for the oxidative stress/inflammation markers from the blood draws, as well as exercise capacity and endurance performance.
How Did NAC Stack Up?
With regard to fatigue and endurance, the study team found that subjects in the NAC group experienced a 66 percent greater improvement in endurance in comparison to the control group on the exercise test designed to stimulate fatigue.
Turning to exercise performance, the NAC group recorded a 7 percent improvement in Vo2max (a measure of exercise capacity), while those in the control group saw their Vo2max fall by 4 percent between the pre- and post-exercise evaluation. While the numbers are small in absolute terms, they are statistically significant in terms of relative performance, especially when one considers that the NAC supplementation was only for seven days and there was no formal exercise program to build Vo2max during the seven-day supplementation regimen.
On the inflammation front, researchers also found that supplementing NAC did improve total antioxidant capacity (TAC) post-exercise (a measure of the total circulating antioxidants available to offset free radicals and thereby reduce oxidative stress). This is an interesting and significant finding in that exercise tends to decrease TAC as available, circulating antioxidants attach to free radical molecules created by muscles/organs burning energy.
At the end of the study, post-exercise TAC in the NAC group was the same as the pre-exercise TAC, implying that the supplemental NAC had protected against oxidative stress created by exercise. By comparison, the control group experienced a significant drop in TAC post-exercise, indicating the body’s antioxidant defenses were suppressed.
Other inflammation markers evaluated in the study also showed NAC supplementation dampened the negative impact of exercise; however, only in one marker (lactate response) did the study team believe the impact to be statistically significant.
Where to Find NAC
NAC is widely available as a stand-alone dietary supplement or as part of broader antioxidant formulas from a variety of online and retail suppliers. It is relatively inexpensive (less than $20 for a 30-day supply) and is tolerated well at the dosage level evaluated in this study.
 Leelarungrayub D, et al. N-Acetylcysteine Supplementation Controls Total Antioxidant Capacity, Creatine Kinase, Lactate, and Tumor Necrotic Factor-Alpha against Oxidative Stress Induced by Graded Exercise in Sedentary Men. Oxid Med Cell Longev. 2011; Epub 2011 Aug 23.