Bioelectrical impedance analysis is more frequently being used to assess body composition in clinical, fitness, and other health-related settings (18-20). What is partially responsible for this increased popularity may be the development of the relatively new contact-electrode systems, leg-to-leg and segmental bioelectrical impedance analysis (LBIA; SBIA). LBIA and SBIA introduce a single-frequency electrical current into the body and measure the impedance to current flow. Fat-free mass, because of its high water and electrolyte content, is highly conductive, whereas adipose tissue is a poor conductor (i.e., higher impedance). This differential response to an electrical current is the basis of the bioelectrical impedance assessment of body composition. These scale-like analyzers differ considerably from the traditional bioelectrical impedance method that requires the accurate placement of gel electrodes at specified anatomic locations. Enhancing their appeal, the LBIA and SBIA analyzers are portable, fast, relatively inexpensive, and require no specialized training to operate.
A potential source of error with bioelectrical impedance analysis may be intra-individual variability in hydration state. Previous research examining the traditional method has demonstrated that impedance is affected by factors that produce shifts in body fluids or electrolytes (8,12,17). Therefore, controlling pretest behaviors that have acute, temporary effects on hydration state is recommended when using bioelectrical impedance for assessment (15,23). For instance, no exercise within 12 hours of the test is a traditional bioelectrical impedance pretest guideline and recommendation of the LBIA and SBIA manufacturer (15). Although subjects may adhere to such restrictions in a controlled laboratory setting, compliance in the field may be unlikely. If necessary, these stringent pretest guidelines significantly reduce the practicality of using the LBIA and SBIA contact-electrode analyzers for body composition assessment in health and fitness facilities.
Current evidence demonstrates that aerobic exercise performed immediately before LBIA and SBIA assessment affects percent body fat (%BF) measurements in both children (2-4,13) and adults (7,9). Demura et al. (7) and Goss et al. (13) reported significant but relatively small decreases in LBIA-measured %BF (≤1.2 %BF) after submaximal and progressive cycle ergometry in healthy adults and children, respectively. Andreacci et al. (2-4) in a series of investigations reported similar reductions in LBIA-measured %BF after laboratory-controlled treadmill exercise and an after-school exercise bout (mean difference ≤1.6 %BF). More recently, we reported reductions in LBIA- and SBIA-measured %BF (mean difference ≤1.8 %BF) after both maximal and submaximal treadmill exercise in adults (9). Collectively, these studies indicate that aerobic exercise performed immediately before assessment reduces the %BF estimate determined by the LBIA and SBIA analyzers.
Resistance exercise, traditionally practiced by relatively few individuals, is now considered an integral component of a comprehensive health-fitness program (1,11,14). Previous research has demonstrated significant fluid movement from the vascular space into active skeletal muscle after resistance exercise (22). Whether the magnitude of the resistance exercise-induced fluid disruption is sufficient enough to alter LBIA and SBIA body composition measurements is unknown and has yet to be investigated. With an increasing percentage of the population participating in resistance exercise and numerous fitness facilities using contact-electrode bioelectrical impedance analyzers to assess %BF, it is important to clarify whether avoiding resistance exercise is a necessary antecedent to the LBIA and SBIA assessment. As such, the purpose of this study was to examine the effect of a resistance exercise bout on %BF measured by LBIA and SBIA in adults.
Experimental Approach to the Problem
This investigation used a within-subjects control group design to examine the effect of resistance exercise on LBIA and SBIA body composition measurements. Each subject reported to the weight training facility on 2 separate occasions: a resistance exercise trial and control trial. The treatment order was determined using a counterbalanced assignment. This design provided the opportunity to evaluate the acute effects of resistance exercise on body composition measures determined by a commonly marketed LBIA and SBIA analyzer.
In total, 86 healthy, recreationally active adults (45 women and 41 men) between 18 and 30 years of age volunteered to participate in this study. The subjects were recruited from 2 weight training and fitness courses where they had received supervised instruction regarding proper lifting form and technique before the experimental trial. Approval from the Institutional Review Board at Bloomsburg University was obtained, and all subjects gave written informed consent before participation. Subject characteristics are presented in Table 1.
After an initial LBIA and SBIA measurement of body mass, impedance, %BF, fat mass, fat-free mass, and total body water, subjects performed 60 minutes of continuous resistance exercise, or did nothing, which served as the control. After the baseline body composition assessment, subjects were provided with a bottle of water (500 mL) for consumption during both trials. Water was provided during the resistance exercise trial to ensure safety and during the control trial to maintain internal validity. The LBIA and SBIA body composition measures were then reassessed 60 minutes after the initial measurement for comparison. During the control trial, subjects sat quietly. Laboratory temperature was maintained at a constant 22°C for all assessments. Urine specific gravity, measured by a hand-held digital fiberoptic refractometer (Misco Corp., Cleveland, OH, USA), was recorded at baseline in a randomly selected subset of subjects (15 women; 20 men) to assess hydration state. Height was determined using a wall-mounted mechanical measuring rod (Seca Corp., Hanover, MD, USA).
Resistance Exercise Session
Resistance exercises were performed at a load equal to 65-75% of 1 repetition maximum (1RM) to allow for the completion of 8 to 12 repetitions per exercise (24). With use of a circuit format, 1 set of 8 to 12 repetitions was performed on the following 8 exercises: bench press, lat pull-down, leg extension, seated row, leg curl, bicep curl, triceps extension, and abdominal crunch. Three full circuits were performed with approximately 2 minutes of rest between each exercise. The protocol, which required 60 minutes to complete, resulted in 3 sets being completed for each exercise in the circuit.
Bioelectrical Impedance Analysis Assessment
Before testing, all subjects were instructed to adhere to the following traditional bioelectrical impedance guidelines (15): a) no food or drink within 4 hours of the test, b) no exercise within 12 hours of test, c) no alcohol consumption within 48 hours of the test, d) empty bladder within 30 minutes of the test, and e) no diuretic medications within 7 days of the test. Subject compliance to these guidelines was confirmed before each experimental trial.
LBIA measurements were determined using a Tanita body fat analyzer, model TBF-300A (Tanita Corporation of America, Inc., Arlington Heights, IL, USA). Each subject, wearing only a t-shirt and shorts, stood erect with bare feet placed properly on the contact electrodes of the LBIA instrument. As previously described (20), the LBIA system consists of 4 contact electrodes (2 anterior; 2 posterior) that are mounted on the surface of a platform scale. A low-energy, single-frequency electrical signal (50 kHz, 500 μA) is passed through the anterior electrode on the scale platform, and the voltage drop is measured on the posterior electrode. Lower-body impedance and body mass were measured simultaneously while the subject stood on the LBIA scale. The LBIA analyzer, using preprogrammed proprietary equations developed by the manufacturer, automatically calculated %BF.
The BC-418 8-contact electrode analyzer (Tanita Corporation of America, Inc., Arlington Heights, IL, USA) was used to collect SBIA measurements. Each subject, wearing only a t-shirt and shorts, stood erect holding the hand electrodes with bare feet placed properly on the contact electrodes of the SBIA instrument. As previously described (21), the SBIA system consists of 4 contact electrodes (2 anterior; 2 posterior) that are mounted on the surface of a platform scale, and each extremity hand-grip has an anterior and posterior electrode. All measurements are carried out using a constant single frequency current (50 kHz, 500 μA). Whole-body impedance is measured as a foot-hand electrical pathway. Similar to LBIA, the SBIA analyzer automatically calculated %BF using preprogrammed proprietary equations developed by the manufacturer.
Data were analyzed using SPSS 11.5 for Windows (SPSS, Inc., Chicago, IL, USA). All values are expressed as mean ± SD. The between-day coefficient of variations (CVs) for LBIA and SBIA were calculated as SD/mean × 100%. Paired samples t-tests were used to detect significant differences in impedance, %BF, body mass, fat mass, fat-free mass, and total body water for each of the experimental trials. The Holm's sequential Bonferroni method was used for control of type I error for multiple comparisons. Bland-Altman plots were used to assess individual differences in %BF pre- to postexercise (5). Scatter plots were used to determine whether baseline hydration state influenced the %BF change during the experimental trials. Statistical significance was established a priori at p ≤ 0.05 for all analyses. The reliability (intraclass correlation coefficient) of the body composition variables determined by LBIA and SBIA for each experimental trial exceeded 0.973.
Data from 27 subjects (13 women; 14 men) who performed the experimental trials on consecutive days were analyzed to determine the between-day CV for each analyzer. The LBIA between-day CVs for %BF ranged from 0.2-9.0% (group mean = 2.3 ± 2.4%) and for impedance ranged from 0.2-6.9% (group mean = 1.8 ± 1.5%). SBIA between-day CVs for %BF ranged from 0.0-7.6% (group mean = 1.8 ± 1.7%) and for impedance ranged from 0.1-3.2% (group means = 1.4 ± 0.9%).
Body composition measurements during the resistance exercise trial are presented in Table 2. Significant reductions in SBIA-measured %BF (women = 0.9%; men = 1.4%), impedance, and fat mass were observed, whereas fat-free mass, total body water, and body mass (women only) significantly increased postexercise in both groups when using the SBIA analyzer. Conversely, no significant differences were observed postexercise for LBIA-measured %BF, impedance, body mass (men only), fat mass, fat-free mass, and total body water in either group when compared with baseline values.
Body composition measurements during the control trial are presented in Table 3. Significant increases in LBIA-measured %BF (women = 0.4%; men = 0.4%), body mass, and fat mass were observed postexercise in both groups. For the SBIA analyzer, significant increases in SBIA-measured %BF (women = 0.6%; men = 0.5%), impedance, body mass, and fat mass were observed, whereas fat-free mass and total body water significantly decreased postexercise in both groups.
Regardless of the analyzer used for assessment, body mass had no apparent influence on the %BF change postexercise during the resistance exercise or control trial (Figures 1 and 2). Total sample differences in %BF pre- to postexercise (mean ± SD) were −0.1 ± 0.7 and 1.2 ± 0.9 for resistance exercise and −0.4 ± 0.7 and −0.6 ± 0.9 for control (LBIA and SBIA, respectively). For the resistance exercise trial, the individual change in %BF pre- to postexercise ranged from −2.3 to 1.5% and −1.9 to 3.5% when using the LBIA and SBIA analyzers, respectively (Figure 1). Eighty-seven percent (LBIA) and 43% (SBIA) of the subjects demonstrated a %BF change of less than ±1.0% after resistance exercise. In comparison, the individual change in %BF after the control trial ranged from −1.8 to 2.2% and −2.6 to 1.8% pre- to postexercise when using the LBIA and SBIA analyzers, respectively (Figure 2). Eight-one percent (LBIA) and 74% (SBIA) of the subjects demonstrated a %BF change of less than ±1.0% after the control trial.
The magnitude of the %BF change was unaffected by the subjects' baseline urine specific gravity measurement during the control (LBIA: R 2 = .004, p = 0.703; SBIA: R 2 = .000, p = 0.972) and resistance exercise (LBIA: R 2 = .008, p = 0.614; SBIA: R 2 = .035, p = 0.280) trials.
The primary finding of this investigation was that impedance and %BF measurements were significantly reduced after resistance exercise when the SBIA analyzer was used for the assessment. Conversely, the resistance exercise bout had no effect on LBIA-measured impedance and %BF values postexercise.
After resistance exercise, significant reductions in SBIA-measured impedance (approximately 22Ω and 22Ω) and %BF (0.9% and 1.4%) were observed in the women and men, respectively. These findings are consistent with our previous work that examined the effect of aerobic exercise on SBIA-measured %BF in adults (9). Dixon et al. (9) assessed 63 healthy, recreationally active adults (31 women; 32 men) before and after a maximal and submaximal treadmill exercise bout. Significant reductions in SBIA-measured impedance and %BF were observed after maximal (approximately 15Ω and 11Ω; 1.0% and 1.0%) and submaximal (approximately 19Ω and 18Ω; 1.2% and 1.7%) treadmill exercise in that study in women and men, respectively. The physiologic responses to an acute bout of resistance exercise have been reported to parallel those observed after endurance-type exercise (6). When assessing body composition using the SBIA analyzer, it is apparent that both aerobic exercise and the resistance exercise bout used presently result in %BF and impedance reductions postexercise. These findings confirm that exercise before SBIA assessment has a significant influence on body composition measures, thereby supporting the traditional bioelectrical impedance pretest exercise recommendation to avoid a temporary alteration in hydration status (15).
Conversely, LBIA body composition measurements were unchanged after the resistance exercise bout. Previously, Dixon et al. (9) reported significant reductions in LBIA-measured impedance and %BF after maximal (approximately 25Ω and 22Ω; 1.8% and 1.4%) and submaximal (approximately 20Ω and 20Ω; 1.5% and 1.2%) treadmill exercise in women and men, respectively. Impedance and %BF reductions were reported for both the LBIA and SBIA analyzers used in that study. Unlike SBIA, which estimates %BF from a whole body impedance measurement using the foot-hand electrical pathway, the LBIA analyzer assesses only the lower extremity. During treadmill exercise, the greatest tissue fluid disruption would most likely occur in the lower extremity because of increased perfusion of active skeletal muscle. As such, this may explain the comparable body composition alterations that were reported for the LBIA and SBIA analyzers previously (9). The current resistance exercise protocol focused primarily on the upper body, incorporating 6 upper- and 2 lower-body exercises. The SBIA analyzer, using the foot-hand electrical pathway, more effectively detected the whole body fluid disruption induced by the resistance exercise bout. With the LBIA measurements conducted only between the legs, the potential resistance exercise-induced fluid disruption of the upper body was not assessed, and impedance was not significantly altered postexercise.
During the control trial, significant increases in LBIA- and SBIA-measured %BF were observed postexercise in both groups. The %BF value, as calculated by the LBIA and SBIA analyzers, is derived from proprietary equations combining impedance and body mass measurements with height, sex, and age information. Therefore, in addition to impedance, body mass changes can affect the %BF estimations. Both analyzers detected a significant increase in body mass (approximately 0.3 kg) after exercise because of the consumption of approximately 500 mL of water. Despite increases in %BF and body mass, impedance was unchanged when using the LBIA analyzer for assessment. This finding is consistent with our previous work that examined the effect of acute fluid consumption on LBIA measurements in 21 recreationally active men (10). In that study, the consumption of 591 mL of water or a carbohydrate beverage had no effect on LBIA-measured lower-body impedance but caused a slight overestimation in %BF (approximately 0.5%) because of increased body mass (approximately 0.5 kg) 60 minutes after drinking. Conversely, the SBIA analyzer in the present study demonstrated significant increases in %BF, body mass, and impedance (mean difference = 5-8 Ω) postexercise. One possible explanation for the apparent sensitivity difference between analyzers is that, once consumed, the fluid takes time to spread throughout the body, and with the LBIA analyzer using a leg-to-leg electrical pathway it is more difficult to reflect whole body changes (7). By measuring whole body impedance (foot-hand), the SBIA analyzer was more sensitive to the fluid alterations induced by drinking during the control trial. Interestingly, although impedance changes were only detected by the SBIA analyzer postexercise, the magnitude of the %BF change was remarkably similar for the LBIA and SBIA analyzers (range = 0.4-0.6 %BF). Therefore, it appears that when using the LBIA and SBIA analyzer-equipped proprietary equations, body mass may be a more important determinant of %BF than impedance.
It is recognized that our findings must be examined within the context of certain design limitations. The moderate intensity of the current resistance exercise protocol, although commonly used during training by recreational lifters, was lower than that incorporated by competitive weightlifters (16). In addition, as previously mentioned, the resistance exercise protocol was upper-body dominant, with only 2 lower-body exercises (leg curl and leg extension). The impact that resistance exercise intensity and exercise selection have on LBIA and SBIA body composition measures cannot be determined from this study. The subjects were also healthy, recreationally active young adults, and, therefore, our findings are not representative of other populations that may differ significantly in age, fitness level, and body composition characteristics. The current bioelectrical impedance pretest guideline recommends that individuals refrain from participating in exercise 12 hours before LBIA and SBIA assessment to control for fluctuations in hydration state (15). Presently, the postexercise assessment was conducted immediately after the resistance exercise bout, and, as such, these findings cannot be generalized to exercise that precedes the assessment by a longer duration. The greatest change in body composition measurements may be expected to occur immediately after exercise because of increases in blood flow to active muscle tissue, cutaneous blood flow, and skin temperature during the exercise bout (17). Nevertheless, the examination of resistance exercise that precedes assessment by a longer duration is warranted to further clarify whether avoiding exercise 12 hours before testing is necessary when using SBIA.
Because of their ease of operation, LBIA and SBIA analyzers are more commonly being used to assess body composition in health and fitness facilities. According to traditional bioelectrical impedance guidelines, it is recommended that clients refrain from exercise before assessment to avoid temporary fluid disruption, which may adversely affect the accuracy of measurement. Our findings indicate that when using SBIA to assess %BF, assessments should be performed before resistance exercise to eliminate potential exercise-induced alterations in body composition measurements. Conversely, the resistance exercise bout had no effect on LBIA measurements postexercise, and, therefore, following the pretest exercise guideline may not be necessary when this technology is used for assessment immediately after the bout. This information is important for coaches, strength and conditioning specialists, personal trainers, athletic trainers, and other health and fitness professionals who currently use this technology to assess or monitor body composition in the field.
The authors gratefully acknowledge Jennifer Nilsen, Jamie Bremen, Lindsay McAndrew, Allen Larsen, and Roxanna Larsen for their assistance in data collection and all subjects for their participation in this investigation.
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Keywords:© 2009 National Strength and Conditioning Association
bioimpedance; body composition; foot to foot