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Ashwagandha Improves Muscle Strength and Recovery in Men Performing Resistance Training

Reviewed: Wankhede S, Langade D, Joshi K, Sinha SR, Bhattacharyya S. Examining the effect of Withania somnifera supplementation on muscle strength and recovery: a randomized controlled trial [published online November 25, 2015]. J Int Soc Sports Nutr. doi: 10.1186/s12970-015-0104-9.

Traditional Ayurvedic medicinal plants are becoming increasingly popular as dietary supplement ingredients in the United States and elsewhere. Ashwagandha (Withania somnifera, Solanaceae) root, one of the most widely used Ayurvedic plants, is considered an adaptogenic herb (i.e., one that helps the body adapt to various types of stress). Although it has been shown to have a wide range of beneficial effects, ashwagandha has not been thoroughly studied for its potential performance-enhancing properties. The authors of this study hypothesized that ashwagandha supplementation would enhance the physiological adaptation of the body in response to the stress of resistance training. Hence, the purpose of this eight-week, randomized, double-blind, placebo-controlled study was to evaluate the effects of a proprietary, standardized ashwagandha extract on untrained men undergoing resistance training.

Healthy men (N = 57, aged 18-50 years) with little experience in resistance training were recruited at a gym in Kolkata, India. Subjects were excluded if they were taking any medication or steroids to enhance physical performance, had lost more than 5 kg (11 lbs) in the previous three months, had a history of drug abuse, smoked more than 10 cigarettes per day, consumed more than 14 grams of alcohol (one “standard” drink) per day, were hypersensitive to ashwagandha, had orthopedic injury or surgery within the previous six months, had participated in other clinical studies during the previous three months, or had any other condition that the investigators deemed problematic. Subjects were instructed not to take anti-inflammatory agents, drink alcohol, or smoke tobacco during the study. No mention was made of screening for intake of known strength-, body composition-, or testosterone-modifying dietary ingredients, such as creatine monohydrate, beta-alanine, or fenugreek (Trigonella foenum-graecum, Fabaceae) seed extract.

Subjects were asked to take either a starch placebo or 300 mg ashwagandha root extract capsule (KSM-66; Ixoreal BioMed; Los Angeles, California) twice daily for eight weeks. The extract was produced using a water-based, “green chemistry” process, and was standardized to contain 5% total withanolides. The authors did not mention if the extract’s chemoprofile was confirmed by a third-party laboratory. During the eight-week study period, subjects participated in a structured resistance training program based on the publications of the National Strength and Conditioning Association (NSCA). Subjects trained three times per week, exercising major muscle groups in both the upper and lower body. During the initial two-week acclimatization phase, each exercise set consisted of 15 repetitions at a lower load to allow the subject’s body and neurological system to adjust to the training. The subsequent six weeks of training consisted of varying numbers of higher-load repetitions.

The primary endpoints were upper-body and lower-body muscle strength. The secondary endpoints were muscle size (measured via tape measure and calipers), muscle “recovery” (defined as reduction of creatine kinase [CK] activity in the blood; CK is leaked from muscle cells after they have been damaged), serum testosterone, and body fat percentage (measured via bioelectric impedance; the machine used was not described). Muscle size was measured at the flexed mid upper arm, chest, and upper thigh. CK activity was measured between 24 and 48 hours after training. Subjects were assessed the first two days after the start of training, and two days after the end of the eight-week training period.

As expected, the resistance training resulted in improvements in all of the measured parameters in both groups. However, the ashwagandha group had a significantly greater increase in upper-body strength (P = 0.001) and lower-body strength (P = 0.04) compared with placebo. The ashwagandha group also had significantly lower blood CK activity (P = 0.03), yet subjective muscle soreness was not described. Compared with placebo, the ashwagandha group had a significantly greater increase in the muscle size of the arm (P = 0.01) and chest (P < 0.001), but there was no significant difference in the size of the upper thigh. Compared to the placebo group, the ashwagandha group had a significantly greater increase in serum testosterone (P = 0.004) and a significantly greater decrease in body fat percentage (P = 0.03). Total body mass (body weight) and fat-free mass changes were not reported. Ashwagandha was well-tolerated, and there were no serious adverse effects.

The authors conclude that “ashwagandha supplementation is associated with significant increases in muscle mass and strength and … that ashwagandha supplementation may be useful in conjunction with a resistance training program.” They acknowledge that the trial was limited by the inclusion of only untrained young subjects, the small sample size, and the relatively short study duration.

A peer reviewer of this Research Review noted that additional weaknesses of the study include: (1) the absence of assessments performed halfway through the study; (2) the lack of reporting of other body composition changes (e.g., fat-free [lean] mass, total body mass, total body water); (3) the lack of independent authentication and phytochemical profiling of the test material; (4) failure to disclose the funding source(s) of the study; (5) a lack of dietary intake data collected over the course of the study, particularly for carbohydrates and protein; (6) lack of serum cortisol measurements (pre-clinical and clinical trial data suggest that ashwagandha can reduce cortisol, which has been shown to correlate with post-exercise CK activity); (7) equating blood CK activity alone as an indicator of “recovery,” coupled with the absence of any functional measures of subjective, athlete-relevant recovery (e.g., muscle strength, soreness, and/or range of motion); and (8) the lack of detailed reporting of the participants’ ages.

The authors of this study do not appear to have any prior research publications that assess muscular performance, post-exercise “recovery,” or body composition in humans, at least insofar as a PubMed search has revealed. Notably, researchers using a powdered whole root ashwagandha extract have reported similar effects on blood testosterone in normal males not engaged in resistance training. Overall, this study lacked sufficient design rigor, methodological detail, and peer review. The authors recommend that further studies evaluate the potential benefits of ashwagandha over longer periods of time and for different populations, including females, older adults, and individuals accustomed to resistance training.

—Heather S. Oliff, PhD