It is well known that obesity is an increasingly prevalent and costly public health issue with many deleterious health consequences across every demographic (4,14,38). Equally understood, physical activity is a key component of obesity treatment and prevention (2,9,11,13,18,19,33,37). Currently, resistance exercise (RE) is increasingly recognized for the unique benefits it may provide to obese populations, which include, but are not limited to increased or maintained lean body mass (LBM), decreased fat mass (FM), improved neuromuscular coordination, enhanced efficiency of metabolic substrates, and improvements in cardiovascular functions (1,2,9,10,13,18,19,33,37). Major health organizations suggest that both endurance and RE are used within weight management programs but are vague on the specifics of these programs.
The general nature of these programs is puzzling because we know that adaptations to RE are specific to the acute program variables (exercise choice, order, intensity, volume, and rest period length) and occur in the activated tissues (3,15,20,32,36). A myriad of RE protocols are used to treat or prevent obesity, but past work has overlooked important components of RE programming (16). This is evidenced by few investigations that properly describe the details of the RE program used when involving obese cohorts, in relation to the acute program variables (30,34,35). Also, it seems that programs tailored to obese individuals prioritize weight loss above all else, and are typified (although anecdotally) by using very high repetitions with very little weight. This is counterintuitive as we know the ability of RE to cause hypertrophy in stimulated muscle (10,32), especially when multiple-sets of 10–12 repetition maximum (RM; ∼70 to 75% of 1RM) are used (3,31). In addition to this, there is a general lack of understanding of how excess FM and the acute program variables interact within a well-designed acute RE protocol.
One area where excess fat mass could logically have an impact is on total exercise volume. In terms of the exercise volume equation (weight or intensity used × repetitions × sets of an exercise), FM could theoretically add to the weight lifted and, according to Henneman's Size Principle (17), could potentially result in greater muscle activation. This fat-mediated increase in activation could then result in increased muscle damage when compared with that of a population that does not have this excess FM. This could especially be true if the RE incorporates eccentric muscle actions. Likewise, another question of practical importance is whether RE results in increased perceptual measures such as soreness, fatigue, and exertion in obese populations, as it is known that pain and soreness are common after RE and are associated with the amount of muscle damage and local inflammatory factors (7,24,29). This is important because these psychological responses can impact future participation in exercise (5,27).
To our knowledge, no investigation has compared muscle tissue damage or perceptual measures in response to a moderately heavy RE protocol, between lean and obese groups. If additional FM effectively adds to the RE load, especially in weight-bearing exercises, there may be more muscle damage, greater perceived exertion, and greater discomfort in populations with obesity when compared with similarly untrained non-obese cohorts. If substantial, these divergent responses may warrant a special approach to RE interventions targeted at the obese. Therefore, the purpose of this study was to compare untrained obese and lean men with regards to muscle tissue damage and perceptual measures during an acute RE protocol that used moderate intensity. We hypothesized that we would observe increased indices of tissue damage through increased loading as a result of higher FM. Accordingly, we also expected to find higher levels of soreness, fatigue, and perceived exertion among the obese men immediately after and in recovery from RE.
Experimental Approach to the Problem
To examine the effects of an acute RE protocol on markers of muscle damage and perceptual measures, we used a balanced, between-group design. The RE protocol was designed to provide a whole-body stimulus that would result in large acute endocrine and neuromuscular responses in addition to continued signs of fatigue and muscular damage 24 hours after exercise.
Nineteen sedentary men participated in the investigation. The subjects possessed no known cardiovascular, endocrine, or metabolic disease and reported the absence of any acute or chronic disease. The subjects also confirmed that they were not taking any medications or dietary supplements, were nonsmokers, and had not lost >2.3 kg (5.0 lbs) at any point in the 3 months preceding the study. Finally, the subjects confirmed that they qualified as being untrained, which was defined as having not participated in resistance training for at least 6 months, or any other structured exercise regimen more than twice per week at a length of 30 minutes per session.
The study groups were similar in terms of physical activity levels, but differed with respect to body mass index (BMI). In line with standards established by the World Health Organization (WHO) to classify obesity status, the participants were designated as “lean” if their BMI was <25 kg·m−2; obese “WHO 1” if their BMI was between 30.0 and 34.9 kg·m−2; and “WHO 2/3” classification if their BMI was >35.0 kg·m−2. The subjects in the lean cohort had significantly lower BMI, FM, and body fat (BF) percentage when compared with both obese cohorts. All the groups displayed nonsignificant differences in 10RM strength (not presented). Statistically significant differences in LBM between the lean and WHO 2/3 groups were present. Subject characteristics are presented in Table 1.
The subjects were verbally instructed on the study procedures, risks, inconveniences, and benefits in an information session. At the end of this information session, each subject volunteered to participate by providing written informed consent and completing a comprehensive medical history form. A physician cleared participating subjects for the absence of disease and fitness for vigorous exercise. This investigation was approved by the University of Connecticut's Institutional Review Board for use of human subjects in research.
Our study design and procedures are reported in more detail elsewhere (34,35) but are briefly described. After a 12-hour fasting period, the subjects reported to the laboratory where height, weight, and circumference (waist and hip) measurements were taken. Hydration status was verified. A dual-energy x-ray absorptiometry (GE Lunar Prodigy Advance, Madison, WI, USA) scan was performed to measure subjects' LBM, FM, and % BF. Analyses of these data were performed by the same technician (blinded to the subjects) using commercial software (Lunar software, encore version 6.00.270).
We used a thorough familiarization process to lessen arousal factors and acquaint subjects with the exercise stress. The familiarization comprised multiple overviews of the study protocol and a thorough explanation of the perceptual scales used throughout the protocol. In addition, the subjects were carefully instructed on how to record and replicate diet, physical activity, and other behaviors before the acute and recovery testing visits. Finally, demonstrations of the selected exercises and ample practice with the exercises were provided under the supervision of a Certified Strength and Conditioning Specialist (C.S.C.S.). Familiarization was complete when the subjects could demonstrate the safe and proper performance of all experimental exercises. If additional familiarization was needed, ample time was allotted for recovery between familiarization visits.
Ten RMs (10RM) were determined for each of the following 6 exercises in the order barbell back squat, barbell bench press, machine double-leg curls, dumbbell 1-arm rows, dumbbell seated shoulder press, and dumbbell step-ups. Again, an extensive familiarization period was used to determine the 10RM for each exercise. Before acute testing, the subjects then preformed the workout to validate the 10RMs and make any final adjustments needed before the first testing session in the experimental sequence. Again, this was done to minimize novel physiological and psychological learning effects to a workout protocol. This extensive familiarization approach provides an important and novel context for which these findings must be placed within for interpretation.
Acute Testing Visit
The acute testing day was completed at least 1 week after the final familiarization visit. All the subjects arrived at the Human Performance Laboratory between 7:00 and 8:00 AM. Each subject had fasted for 12 hours, and abstained from alcohol, caffeine (not >2 cups), and strenuous physical activity for 24 hours, before the test day. The subjects arrived in a euhydrated state (confirmed by urine specific gravity of <1.020, via a refractometer; Model A300CL, Spartan, Japan). Physical activity and diet records were then collected to confirm compliance with study controls. The same research team performed all the test trials.
The subjects equilibrated for 15 minutes in a semireclined position, after which a trained phlebotomist inserted a flexible, indwelling Teflon cannula into a superficial forearm vein. A 3-way stopcock was connected to the end of the catheter to allow for multiple blood samples from the same vein. This setup was kept patent with 1:10 heparin-saline solution. After an additional 10 minutes of equilibration, a preexercise (PRE) blood sample was obtained. Plasma myoglobin and serum creatine kinase (CK) were obtained before (PRE), exercise or immediate post (IP) and in recovery from exercise (at +110 minutes and 24 hours after exercise). The subjects were encouraged to drink water ad libitum throughout the protocol. Whole blood was collected and placed in serum tubes, for CK, or plasma tubes (with ethylenediaminetetraacetic acid) for myoglobin. The samples were then centrifuged, aliquoted, and stored at −80° C until subsequent analyses were conducted.
Resistance Exercise Protocol
The RE protocol was adapted from Silvestre et al. (30) and used mostly free-weight exercises to stimulate all major muscle groups at an intensity of 85–95% of subjects' 10RM. A standardized warm-up was completed directly beforehand. The following 6 exercises used 3 sets of 10 repetitions in the following order: barbell back squat, barbell bench press, machine double-leg curls, dumbbell 1-arm rows, dumbbell seated shoulder press, and dumbbell step-ups (this last exercise differed from that of Silvestre and was selected to provide a stronger muscle stimulus). One warm-up set of 60% of the previously determined 10RM was used before the squat and bench press exercises. Two minutes of rest was provided between each set of Squat and Bench Press. Ninety seconds of rest was allotted between every set of the remaining 4 exercises (30).
Twenty-four hours after the completion of the exercise protocol, the subjects returned for Recovery testing. The subjects confirmed that they had repeated the diet and alcohol, caffeine, and activity requirements used before the acute testing visit. Following processes identical to those used during the acute testing visit, perceptual scales were administered and a 10-ml blood sample was obtained from an antecubital vein and processed in the same manner as the acute testing visit.
The subjects completed 3 muscle soreness and fatigue scales before (PRE), immediately after (IP), and 24 hours after exercise (+24). These scales consisted of (in order): one 10-cm line Likert “Pain and Soreness” scale (21,22); one 10-point Likert “Fatigue” rating scale; and one 10-point Likert “General Soreness” scale (22). Additionally, the subjects were instructed to rate their exertion after each set of the aforementioned exercises within the RE protocol using the CRQ-10 scale (25).
Myoglobin samples were analyzed in duplicate by an enzyme-linked immunosorbent assay (Alpco, Salem, NH, USA). According to the manufacturer, the sensitivity of the assay was 6.25 ng·ml−1. Intraassay coefficient of variation was 11.3%, and interassay coefficient of variation was 7.7%. Creatine kinase samples were analyzed in duplicate via spectroscopy (Genzyme Diagnostic, Charlottetown, Prince Edward Island, Canada). All the samples were thawed only once before they were analyzed.
Data are presented as mean ± SD unless otherwise noted. All data were checked for normality and homogeneity of variance. For variables that violated these assumptions, data were logarithmically (log10) corrected, before analysis, and reanalyzed. Data were analyzed using a 2-way analysis of variance with repeated measures. When appropriate, a Fisher’s least significant difference post hoc analysis was performed to determine the nature of pairwise differences. Statistical significance was set at p ≤ 0.05 for this study.
The primary findings of this investigation were that (a) myoglobin and CK levels were not significantly different between the groups in response to moderately intense RE, (b) no significant differences were found between groups with regard to perceived exertion during exercise or perceived soreness and fatigue after exercise, and (c) when volume of exercise is compared between groups relative to FM, significant differences in total volume were observed between all 3 groups, where the highest volume was observed in the WHO 2/3 group and the least volume in the Lean group.
Muscle Damage Markers
Myoglobin and CK results are presented in Table 2. For myoglobin, the interaction for group × time was not significant (F = 0.93, degrees of freedom [df] = 6, p = 0.49); however, a significant main effect for time was present within groups (F = 27.48, df = 3, p < 0.01). Likewise, for CK, the group × time interaction was not significant (F = 1.18, df = 6, p = 0.33), yet there was a significant main effect for time (F = 14.99, df = 3, p < 0.01).
Perceptual scale data are summarized in Table 3. There were no group × time interactions for either the Pain and Soreness (F = 0.33, df = 4, p = 0.86), Fatigue (F = 1.04, df = 4, p = 0.40), or General Soreness scales (F = 0.83, df = 4, p = 0.52). Ratings in all scales increased significantly directly after completion, these elevations did not persist uniformly among all groups at 24 hours after exercise. As expected, ratings of perceived exertion increased after each set but the 2 groups did not differ significantly (F = 0.99, df = 2, p = 0.390). Specifically, average rating of perceived exertion for the groups was as follows: Lean = 8.0 ± 0.59, WHO 1 = 7.7 ± 0.97, and WHO 2/3 = 7.4 ± 1.01. Lactate concentrations were not different between the groups either (not presented). Therefore, both groups appeared to experience similarly elevated levels of metabolic and psychological stress, and soreness and fatigue 24 hours after the protocol.
Ten Repetition Maximum Strength, Volume, and Fat Mass
The 3 groups did not display significant differences in 10RM for any of the 6 exercises (Table 4). Also, total volume lifted (weight lifted × number of repetitions × number of sets) was similar, as was volume on each individual exercise (not presented). Overall, these results indicate that the 3 groups completed a similar amount of total work. Because both the WHO 1 and WHO 2/3 groups had a significantly greater FM than did the lean group, we also analyzed the volume data after adding the FM to the load of the weight-bearing exercises of squat and step-ups. We did this to determine if noncontractile FM added significant volume to these exercises. As expected, for total volume + FM, significant differences were observed between all 3 groups (Lean and WHO 1, p = 0.013; Lean and WHO 2/3, p < 0.01; WHO 1 and WHO 2/3, p = 0.028).
Contrary to our hypothesis, when compared with men who are lean, men who are obese in both the WHO 1 and WHO 2/3 groups displayed similar indices of muscle tissue damage, perceived exertion, soreness, and fatigue. Additional FM did, however, result in significantly greater volume within the primary weight-bearing REs (squat and step-ups), and this impacted total exercise volume.
We predicted that excess FM would increase muscle damage as a result of a higher load and thus greater total RE volume. As measured by myoglobin and CK, two of the many skeletal muscle constituents released with damage to the sarcolemma, this was not the case. Creatine kinase a larger molecule, increases up to 5 days after an RE stimulus (7), so we might have missed peak concentrations of this muscle damage marker. We consider this unlikely because differences, if robust, would have been indicated at our 24-hour postmeasurement recovery time point. Additionally, our myoglobin data corroborate this lack of difference of muscle damage between the groups, because it is viewed by some as a more sensitive marker of muscle damage (owing to its smaller molecular weight and its typical return to baseline within 24 hours after RE) (12,39).
Alternatively, the well-known intersubject variability of CK (7,8,26) could also partially explain our unexpected findings. As an example, if 1 subject in the lean group was an outlier in terms of displaying high CK values at a given time point; their result could skew the overall values of the lean group, leading to a spuriously high group value. After identifying and removing the presence of this single outlier in our lean group sample, the overall findings of our investigation were unaffected; this makes this possible explanation unlikely. Future studies may choose to use larger n sizes, which would lessen the possible influence of such outliers.
Perceptual scales can be instructive, especially when used to characterize a RE stimulus in a unique population, such as the one used in this study. The lack of difference between the lean and obese groups suggests that such perceptions reflected the untrained status of the 2 groups overall, and not the increased volume of exercise performed by our obese groups during the weight-bearing exercises, as we would have expected. Additionally, ratings of perceived exertion displayed similar patterns throughout the protocol, and were supported by similar lactate concentrations among all groups (not reported). The relationship between lactate (metabolic challenge), damage, and perceived soreness, fatigue, and exertion warrants further investigation in obese populations. However, the results of the current investigation indicate that perceptions of exertion, fatigue, and soreness reflected the untrained status of the groups.
In absolute terms, our groups were similar in 10RM strength for all the exercises and exercise volume. Upon manipulation of the volume data to include excess FM, especially during weight-bearing exercises, men who were obese within both WHO distinctions had similar indices of muscle damage and soreness. This is surprising because muscle damage is related to muscle activation, and increasing exercise load increases muscle tissue activation (17,23,32). The lack of difference between the groups despite a higher volume relative to FM leads us to believe that the presence of excess FM during every day activities (such as standing up, walking up and down stairs, etc.) could potentially cause a protective training effect, much like the repeated bout effect described in the literature (6,7). In addition, it is known that with RE training, less muscle mass can be used to lift the same amount of weight, which before training stimulated relatively more muscle mass (28). This could very well be the case in our study, as both obese groups had a higher volume (relative to FM) than the lean groups did, yet displayed similar muscle damage marker and perceptual responses.
The comparison of acute responses to moderately intense RE among obese and lean subjects is relatively novel (5,16,27,34,35), but the potential influence of other upper regulatory elements, as described by Spiering et al. (32), must be considered. Some of the subjects had past experience with RE, although this potential confounder was minimized by assuring that the subjects were not currently involved in any formal RE. Additionally, the age of our subjects (and duration or severity of obesity) must also be contextualized. Physiological differences in younger obese men may not be as significant as those found in older cohorts, where large and well-known disruptions in metabolic and hypothalamic-pituitary-adrenal activities are observed (34,35). Considering the general lack of well-characterized responses to RE of obese men, further research to determine specific interactions between this population and the acute program variables (exercise choice, volume, intensity, order, and rest) is necessary and vital to understanding the benefits RE can have for obese populations.
In summary, excessive FM increases the total volume of a moderately intense RE workout but obesity may result in protective adaptations that lessen muscle tissue damage when compared with a similarly untrained lean cohort. Differences in BMI, FM, and % BF do not appear to significantly affect perceptual indices of exertion, soreness, or fatigue. Further work using different acute program variables and upper regulatory elements is needed, but our findings demonstrate that untrained, non-elderly men who are obese tolerate relatively high intensity RE and similar to untrained men who are lean. Furthermore, in the absence of other comorbidities and factors, free weights and moderate loads should not be avoided in exercise interventions for obesity. In addition to providing an insight into the increasingly common practice of RE interventions for weight management programs, this manuscript strengthens the link between exercise physiology and the urgent health concerns relative to obesity research.
This investigation provides novel insight into the acute muscle damage and perceptual responses of subjects who are obese to moderate-intensity RE. Although precaution and consideration to other conditions and comorbidities must be made, our findings suggest that untrained obese individuals respond to RE in a similar or even preferable manner to lean and untrained cohorts. Free-weight RE of moderate to high volume should therefore not be categorically avoided, as individuals with obesity may have much to gain from the beneficial stimuli this style of exercise provides.
The authors would like to thank the dedicated group of test subjects and our research and medical staff who all made this project possible. The authors have no conflicts of interest, and financial support funding was provided by internal laboratory funds. The results of this study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association.
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