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Blood Lactate and Hormonal Responses to Prototype Flywheel Ergometer Workouts

Caruso, John F1; Coday, Michael A1,2; Monda, Julie K3; Ramey, Elizabeth S1; Hastings, Lori P1; Vingren, Jakob L4; Potter, William T4; Kraemer, William J2; Wickel, Eric E1

Journal of Strength and Conditioning Research: March 2010 - Volume 24 - Issue 3 - p 749-756
doi: 10.1519/JSC.0b013e3181c6cfb3
Original Research
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Caruso, JF, Coday, MA, Monda, JK, Ramey, ES, Hastings, LP, Vingren, JL, Potter, WT, Kraemer, WJ, and Wickel, EE. Blood lactate and hormonal responses to prototype flywheel ergometer workout. J Strength Cond Res 24(3): 749-756, 2010-The purpose of the study was to compare blood lactate and hormonal responses with flywheel ergometer (FERG) leg presses for preliminary assessment of workouts best suited for future in-flight resistance exercise. Comprised of 10 repetition sets, the workouts entailed 3 sets of concentric and eccentric (CE3) actions, or concentric-only actions done for 3 (CO3) or 6 (CO6) sets. Methods employed included assessment of blood lactate concentrations ([BLa]) before and 5 minutes postexercise. Venous blood was also collected before and at 1 and 30 minutes postexercise to assess growth hormone, testosterone, cortisol concentrations ([GH], [T], [C]) and [T/C] ratios. [BLa] were compared with 2 (time) × 3 (workout) analysis of variance. Hormones were assessed with 2 (gender) × 3 (time) × 3 (workout) analysis of covariances. Results showed [BLa] had a time effect. Growth hormone concentration showed gender × workout, gender × time, and workout × time interactions, whereas [T] had a 3-way interaction. [C] had gender, time, and workout effects. [T/C] yielded a gender × time interaction. It was concluded that, because CO6 and CE3 yielded similar anabolic hormonal data but the latter had a lower [C] 30 minutes postexercise, CE3 served as the best workout. Although the FERG was originally designed for microgravity, the effort put forth by current subjects was like that for workouts aimed at greater athletic performance and conditioning. Practical applications suggest that eccentric actions should be used for FERG workouts geared toward muscle mass and strength improvement.

1Exercise Physiology Laboratory, Exercise and Sport Science Program, The University of Tulsa, Tulsa, Oklahoma; 2Department of Kinesiology, The University of Connecticut, Storrs, Connecticut; 3Department of Chemistry and Biochemistry, The University of Tulsa, Tulsa, Oklahoma; and 4Department of Kinesiology, Health Promotion and Recreation, University of North Texas Denton, TX

Address correspondence to Dr. John F. Caruso, john-caruso@utulsa.edu.

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Introduction

The knee extensors are a muscle group prone to space flight-induced mass and strength losses (8,16). Greater losses generally occur with longer flights, with the rate of strength loss exceeding that for muscle atrophy (7,16). The stimulus for in-flight knee extensor losses is a lack of mechanical loading (16). Thus, devices that operate without standard gravitational resistance, yet impose high mechanical loads, are best suited for space flight. Because resistive exercise offers a more intense mechanical load stimulus than aerobic activity (16), and because the former modality evokes muscle mass and strength gains in ambulatory subjects (1,23,34,35), it shows promise as an in-flight treatment to reduce some of the adverse effects of microgravity. An ergometer (YoYo Inertial Technologies, Stockholm, Sweden, Figure 1) equipped with 2 flywheels was suggested as a countermeasure to in-flight mass and strength losses (5). The device in Figure 1, which operates without gravity, offers more eccentric resistance than standard free weight equipment (5). The merits of the flywheel ergometer (FERG) to reduce strength losses in a 40-day ground-based microgravity analog were assessed and showed that the device offered a substantial mechanical load stimulus to the unloaded knee extensors (8).

Figure 1

Figure 1

Although the imposition of greater mechanical loads reduces in-flight mass and strength loss, other factors may foretell the efficacy of FERG workouts. Such factors include the hormonal milieu that results from specific workout protocols. Because hormones bind to their respective skeletal muscle receptors in response to exercise, they foretell the merits of various workouts to abate mass and strength losses. In addition to the type of workout performed, temporal and gender-based considerations influence hormonal concentrations. Anabolic hormone (testosterone, growth hormone) secretion, in addition to the mechanical loads imposed, augments in-flight mass and strength loss attenuation. Conversely, secretion of the catabolic hormone cortisol must be minimized to limit mass and strength losses. Space travel, with or without concurrent in-flight exercise, alters plasma concentrations of many hormones (22,36,37,45). Such changes parallel those for blood lactate, an anaerobic metabolite (22,48). The degree by which blood lactate concentrations ([BLa]) are altered by microgravity has been mixed (22,48). Resistive exercise intensity and volume impact [BLa] (1-4). Thus, [BLa] and the aforementioned hormones act as important markers to limit in-flight knee extensor mass and strength losses.

The merits of FERG workouts were assessed in ambulatory and ground-based microgravity simulation models (7-10). In addition, the FERG was examined for its utility in Earth-bound applications, such as to abate musculoskeletal losses in the elderly (6). Yet, research has not compared hormonal responses with various workouts done on the FERG. Because a modified FERG is to be used on the International Space Station (17), and flywheels offer a mechanical loading stimulus to the National Aeronautics and Space Administration's in-flight advanced resistive exercise device (39), the current study purpose compares hormonal and [BLa] from leg press workouts done on the Figure 1 prototype FERG. Although the current study does not use microgravity simulation, results may offer baseline knowledge on hormonal and [BLa] responses from different workouts to aid the design and implementation of future in-flight resistive exercise protocols. Of the 3 current FERG workouts to be compared, we hypothesize one will evoke a mechanical loading stimulus that offers a hormonal and [BLa] milieu best suited to abate future in-flight mass and strength losses.

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Methods

Experimental Approach to the Problem

To determine a protocol best suited to abate future in-flight mass and strength losses, subjects (14 men, 14 women) performed 3 FERG workouts and submitted to [BLa] assessments pre-exercise and 5 minutes postexercise. A subset (7 men, 10 women) also submitted to venous blood draws before and at 1 and 30 minutes postexercise to assess growth hormone, testosterone, and cortisol concentrations ([GH], [T], [C]) and to derive [T/C] ratios. Comprised of 10 repetition sets, workouts entailed (a) 3 sets of concentric and eccentric (CE3) actions, (b) concentric-only actions for 3 (CO3), or (c) 6 (CO6) sets. Workouts were spaced at least 1 week apart to limit training adaptations and randomized to prevent an order effect. CE3 and CO6 workouts entailed similar volumes of work and roughly twice that of the CO3 protocol (10). Thus, the current design enabled comparison of contractile mode and volume influences to be assessed. Current study-dependent variables included blood lactate, hormonal, and FERG performance measures. Gender, time, and workout served as independent variables.

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Subjects

Subjects were informed of the experimental risks and signed an informed consent document before their participation. All procedures were approved by a university-based institutional review board for the use of human subjects before data collection. Current subjects were free of lower body musculoskeletal injuries that may have impaired their workout performance. Because it does function like standard free weight equipment, before the start of FERG workouts, subjects performed a familiarization session to become accustomed to the operation of the device and reduce their risk of injury. Our sample included 6 varsity athletes and 5 habitual resistive exercise participants. Yet none had prior FERG experience, hence the need for familiarization sessions. Subjects refrained from exercise (mean ± SEM) 36 ± 2 hours before workouts and had body masses of 84.9 ± 4.1 kg (men) and 66.2 ± 2.3 kg (women).

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Procedures

Ergometer resistance comes from 2 flywheels. They are joined by an axle and rotate in unison. A nylon strap connects the footplate and flywheels, so resistance is imparted with each repetition. Subjects exerted forces against the footplate. Because concentric forces exceeded the resistance, flywheels and axle rotate at rates commensurate with the forces exerted. Because rotation occurs, the cord unwraps from the axle to permit force exertion as the knees extend. Upon full extension, kinetic energy imparted by flywheel rotation reverses footplate movement as the strap rewraps around the axle (5). Eccentric forces were then exerted to slow the footplate's return motion and impede flywheel rotation, as done for the CE3 protocol. In contrast, subjects refrained from eccentric force exertion as kinetic energy reversed footplate direction and the strap completely rewrapped around the axle (CO3 and CO6 protocols). The level of eccentric resistance was reliant on the flywheel velocity attained by the prior concentric action. Maximal-effort concentric FERG actions thus offered a greater eccentric load than free weight equipment (5).

To measure performance, a permanent magnet motor was mounted on the FERG. The motor had a metal shaft with a small rubber wheel on its terminal end that abutted, and rotated concurrently with, 1 flywheel. With rotation, electrical current from the motor was fed into a card interfaced with software (Model 6.1, Labview, Austin, TX, USA) that collected data at 10 Hz. Figure 2 illustrates a repetition waveform. The ascendent slope is from a concentric action whereby muscle shortening increased rotational rates. Such actions concluded with the highest rotational rate attained, termed the peak angular velocity (PAV). The descendant slope is from an eccentric action that slowed flywheel rotation and the footplate's return and coincided with the start of a new repetition.

Figure 2

Figure 2

Work was measured as

, where I equals flywheel inertia and ω denotes the highest rotational rate (PAV) per repetition. Per FERG protocol, the above equation calculated work per repetition and then summed to derive total work (TW). The above formula measured work from concentric and eccentric actions; the latter calculated only for CE3 workouts. Differences in peak and lowest velocities (Figure 2) represent the lengthening forces exerted; that value was entered into the above formula (ω) to measure eccentric work for the CE3 protocol. Per FERG protocol, PAV is an index of the highest force exerted and workout intensity, whereas TW denotes volume of exercise performed.

At the start of workouts, all subjects first submitted to pre-exercise blood draws to assess [BLa]. Subjects then began a stationary cycle warm-up for 5 minutes against 9.8 N of resistance at a self-selected velocity. At that time, they were randomized to a specific FERG workout. Subjects were instructed to exert maximal voluntary effort throughout workouts and received 90-second rests between sets. After workout completion, subjects submitted to a [BLa] assessment 5 minutes postexercise. [BLa] were assessed from a fingertip blood drop (∼25 μL) with a calibrated analyzer (Accusport, Sport Resource Group, Hawthorne, NY, USA). A subset of subjects (7 men, 10 women) also submitted to ∼3-ml antecubital venous blood draws before and at 1 and 30 minutes postexercise. Blood was collected in 4-mL Vacutainer tubes (Ref 367844, Franklin Lakes, NJ, USA) with 7.2 mg of K2 EDTA. Samples were immediately iced and later centrifuged at 3,000g for 15 minutes. Plasma was then placed in labeled Eppendorf tubes and frozen at −80°C for later analysis. Plasma T, C, and GH were assayed in duplicate with enzyme-linked immunosorbent assay kits (Diagnostic Systems Laboratories, Webster, TX, USA). All samples were measured in the same assay. Intra-assay variance was 8.3, 7.2, and 4.7% for T, C, and GH, respectively. Assay sensitivities were 0.14 nmol·L−1, 2.76 nmol·L−1 and 0.03 g·L−1 for T, C, and GH, respectively.

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Statistical Analyses

Data were initially examined for statistical outliers with Z-scores. Outliers were omitted from analysis. Peak angular velocity and TW means were each compared with 2 (gender) × 3 (workout) analysis of variance (ANOVA), with repeated measures for workout. Mean [BLa] were compared with a 2 (gender) × 2 (time) × 3 (workout) ANOVA, with repeated measures for time and workout. Plasma [GH], [T], [C], and [T/C] were each assessed with 2 (gender) × 3 (time) × 3 (workout) analysis of covariances, with repeated measures for time and workout. Subject's pre-exercise values served as covariates for each hormonal analysis. An α ≤ 0.05 and Tukey's post hoc were employed on all statistical analyses. With the large effect sizes from resistive exercise (34), and α and β values of 0.05 and 0.80, respectively, the sample size met our power analysis needs and enabled detection of significant mean differences and an equal delineation of type I and II error rates. The reliability of current study hormonal (31), [BLa] (10), PAV (10), and TW (9) measures were previously reported.

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Results

No subjects were injured from workouts. Data met most ANOVA assumptions, yet [GH] were not normally distributed; thus, values were converted to their logarithmic base 10 values for statistical analysis (43). Z-scores showed [T] (and the resultant [T/C] ratio) from 1 subject was a statistical outlier. Two subjects voluntarily withdrew before their project completion; they missed a total of 3 workouts. Peak angular velocity and TW each showed gender (men > women) effects. Total work also had a workout (CE3, CO6 > CO3) effect. [BLa] showed a time (post > pre) effect. [GH] had gender × workout (women > men for CO6 and CO3), gender × time (women pre-exercise > the other means), and workout × time (1 minute postexercise: CO6 > CE3, CO3; 30 minutes postexercise: CE3 > CO3) interactions. [T] yielded a 3-way interaction, with male CE3 and CO6 data at 1 and 30 minutes postexercise revealed as the interaction source. [C] had gender (men > women), time (1 and 30 minutes postexercise > pre-exercise), and workout (CO6 > CE3, CO3) effects. [T/C] analysis showed a gender × time (men: pre-exercise > 1 minute postexercise > 30 minutes postexercise; women: unchanged) effect. Peak angular velocity, TW, [BLa], and hormonal data appear in Tables 1-7.

Table 1

Table 1

Table 2

Table 2

Table 3

Table 3

Table 4

Table 4

Table 5

Table 5

Table 6

Table 6

Table 7

Table 7

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Discussion

Our study compared blood lactate and hormonal data from a device initially intended as an in-flight countermeasure for knee extensor mass and strength losses. Each dependent variable shows a certain degree of statistical significance. Peak angular velocity and TW gender differences are likely because of the higher body and/or muscle mass of male subjects (18,40). Peak angular velocity data showed no interworkout differences, which suggests that intensity was similar across protocols. Total work results show a workout effect, an expected outcome of the current design. CE3 and CO6 workouts had twice the TW volume of CO3, yet CO6 was solely a muscle shortening effort, whereas CE3 included equal numbers of concentric and eccentric actions. A comparison of current study workout data allows exercise volume and contractile mode influences upon lactate and hormonal responses to be examined.

Despite higher CE3 and CO6 TW values, [BLa] only show a time effect. [BLa] increases were 220% (CO3), 289% (CE3), and 300% (CO6). Similar interworkout intensities and data variability may have caused insignificant [BLa] differences. Although space travel increases [BLa] (22), in-flight exercise does not raise metabolite levels beyond those seen from ground-based workouts done at similar intensities (48). Current [BLa] concur with ground-based data (3,11) and are indicative of the type of protocol performed. Like current workouts, hypertrophy protocols (8-12 repetition sets done to failure, interspersed by 60- to 120-second rests) evoke high [BLa] (29,34,35). Yet with a protocol similar to the current study, 2 elbow flexor workouts, each comprised of 3 sets done to momentary failure against different (90 and 100% of 10RM) loads led to a small but significant time (post > pre) effect (4). Although [BLa] rose more with 90% load (118 vs. 58%), no significant interworkout differences occurred (4). Lighter loads permitted performance of more repetitions, which led to higher [BLa] (4). Differences in percentage [BLa] increases among the current and prior (4) studies may be because of the exercise examined, because larger muscle masses normally yield higher lactate production.

Exercise entails reliance on anaerobic glycolysis whose products include lactate and H+, which are each correlated to [GH] (20). Limited in-flight data suggest that [GH] are not elevated, which contribute to muscle mass and strength losses (37,45). Although in-flight cycle ergometry (n = 1) led to higher [GH] vs. a similar exercise workload done 3 weeks before space travel (36), the reverse was true from exercise (n = 4) on a torque-velocity dynamometer (37). It was concluded that a minimal level of neuromuscular activity and mechanical loading was needed for in-flight exercise; if that threshold was not met, lower [GH] ensued (37). Table 4 shows that women had higher initial [GH], likely from estrogen-based sensitization to somatotrophs (19,34,44,47). Yet compared with pre-exercise data, men had higher percentage increases over time. This likely occurred because men (a) had much lower initial [GH] and (b) yielded higher TW (Table 2) values from FERG exercise (1,2,19,20,34,42,46). Table 4 includes a workout × time effect, with CO6 > CE3, CO3 at 1 minute postexercise but CE3 > CO3 after 30 minutes. Postexercise [GH] usually peak within 15 minutes because of the volume of work performed (1,2,19,34,44). Although the CO6 workout provided an expected response, whereby a higher TW volume evoked a greater [GH] at 1 minute postexercise and the latter declined (33,45), CE3 had the opposite effect, which suggests that eccentric actions delay postexercise [GH] increases.

Eccentric FERG loads are dependent on forces exerted from the prior concentric action. Maximal force exertion on the FERG evokes more eccentric resistance than standard devices (5). Acute studies examined contractile mode and [GH] (14,28,29,34). One study assessed postexercise [GH] from single blood draws (34), whereas others compared muscle actions done against absolute (14,28), or relative loads (29) via multiple draws that never occurred beyond 15 minutes postexercise. Eccentric actions yielded modest [GH] gains that quickly peaked and then subsided (14,28,29), unlike CE3 data. Yet a study saw large [GH] changes by contractile mode from chronic resistive exercise protocols that were comprised of different amounts of concentric and eccentric actions held constant over a 19-week workout period (31). Results showed that posttraining [GH] gains were contractile mode specific and unlike those from acute studies (14,28,29,31,34). Performance of both concentric and eccentric actions within a single workout, as done with the current CE3 protocol but not in prior acute studies (14,28,29), may impede GH release, though this is unproven. A more likely cause is muscle proprioception, which promotes GH release more than lactate (20,21). Eccentric FERG actions may increase proprioception to yield a delayed, yet greater, GH release 30 minutes postexercise (21). Because the current study did not measure proprioception, this mechanism is speculative but deserves inquiry.

Current [T] yielded a 3-way effect, with male CE3 and CO6 data at 1 and 30 minutes postexercise shown as the interaction source. Gender-related [T] differences concur with prior studies (26,34). Less understood is the impact of various resistive exercise protocols on [T]. A comparison of concentric- vs. eccentric-induced changes showed that either muscle action, whether against an absolute (14) or relative (29) load, evoked greater [T] postexercise. Yet [T] returned to pre-exercise values 15 minutes after workouts (14,29). Postexercise differences among the current and prior studies may be because of intensity-mediated changes in sympathetic activity (15). Perhaps the current study, which entailed a single exercise done at a higher intensity than earlier studies (14,29), led to more localized fatigue and greater sympathetic activity that augmented postworkout [T] (14). CE3 and CO6 protocols, each with a higher TW volume than CO3, evoked greater [T] (34). Yet among protocols with similar TW values, those done at higher intensities elicit greater [T] (1). A comparison of 2 exercise protocols with similar work volumes, whereby one included spotter-assisted repetitions performed beyond momentary failure, whereas the other did not, showed that the former yielded higher [T] (1). Thus, current results, whereby CE3 and CO6 protocols yielded similar PAV values and higher TW than CO3, evoked higher [T] to concur with prior studies (26,34).

[C] shows gender, time, and workout effects. The high current pre-exercise values may be because of greater sympathoadrenal activity that evoked epinephrine secretion (15). To abate in-flight muscle mass and strength losses, protocols should be devised that blunt [C]. Gender-based [C] differences from exercise are likely because of higher male workout intensities. For instance, PAV had a gender (men > women) effect that parallels current [C] changes. The rigor of FERG workouts also contributed to the current time effect. Research notes workouts against heavy loads evoke time effects, because athletes will incur higher [C] than sedentaries who perform similar protocols (23,25,30-33,38). Finally multisprint (32,41) and 2-hour running protocols (12) each elevated [C], because the former produced values like current results. Thus, the stress of current workouts performed at similar intensities yielded results that concur with prior studies (12,23,25,30-33,38,41).

[C] shows a workout (CO6 > CE3, CO3) effect. Despite similar CE3 and CO6 TW values, only the latter yielded higher [C] than CO3, which suggests eccentric actions blunt [C]. Prior work shows a lower metabolic cost from eccentric actions (9,13). Perhaps [C] changes from eccentric actions are dictated by metabolic factors in addition to TW. Metabolism research showed eccentric actions evoked 1/7th the net energy cost of muscle shortening from leg presses done on standard equipment (13). In a similar fashion, eccentric FERG leg press actions added no net caloric cost beyond that from concentric exercise (9). It was concluded the CE3 protocol uses stored elastic energy to evoke muscle potentiation and stretch reflexes with eccentric FERG actions (9). Future research on the impact of eccentric actions on metabolism and [C] is warranted.

[T/C] ratios assess the relative anabolism/catabolism incurred from various treatments. Table 7 shows large post-workout cortisol increases in men, while women's values show insignificant changes. [T/C] ratios were previously monitored in male athletes before and after a sprint protocol with repetitive 20-second runs separated by 100-second rests (41). The repetitive design of the sprint protocol is similar to the current study, yet sprint results led to a 21% [T/C] increase, unlike current outcomes (41). Differences between the current and sprint studies are in part because of variations in exercise intensity. Current subjects were told to exert maximal voluntary effort, whereas sprinters ran at a myriad (56-100%) of intensities (41). Lower sprint intensities imposed less stress and [C] that in turn yielded an elevated [T/C] (41). Yet lower PAV data from our female subjects suggest that a reduced exercise intensity yielded smaller [C] and left [T/C] unchanged. Thus, exercise intensity variations may account for [T/C] differences in the current and prior studies (41).

Our study design sought to identify the best workout, in terms of mechanical loads imposed and the resultant hormonal milieu, for baseline knowledge of future in-flight resistive exercise programs. Workouts on standard resistive exercise devices showed that hormonal responses generally differed little by contractile mode (29-31). A resistive exercise study that compared hormonal responses done against absolute loads showed greater [GH] from concentric actions, yet the effect was attributed to intensity rather than contractile mode (14). CE3 and CO6 workouts yielded similar [T] changes; yet in terms of [GH], the former protocol evoked the highest 30 minute postexercise value and did not contribute to the gender × workout interaction. In addition to 30 minute postexercise [C] data (CO6 > CE3, CO3), results imply CE3 is the best of the examined workouts. Future International Space Station workouts hope to use a modified FERG that offers less eccentric resistance than the Figure 1 prototype to limit spacecraft vibration (17).

Although minimization of in-flight vibration is a valid concern, current data suggest that reduced eccentric resistance may compromise the resultant hormonal milieu. Current results should be interpreted with caution, because continued research is needed to ascertain an ideal resistive exercise protocol to abate in-flight mass and strength losses. Future research may include microgravity simulation to make results more applicable to space flight.

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Practical Applications

Based upon the mechanical loads imposed and the resultant hormonal milieu, current results suggest that FERG workouts should include eccentric actions. Many athletic endeavors and conditioning programs include eccentric actions as a regular part of workouts. In contrast to standard resistive exercise devices, the FERG provides greater eccentric resistance. Programmatic needs of athletes will differ based upon the requirements of their chosen sport, but for those who wish to include FERG protocols for added muscle mass and strength, eccentric actions should be used.

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Acknowldegments

We wish to thank our subjects for their participation. Funding was provided through a University Faculty Development Fellowship Program. John F. Caruso, Michael A. Coday, and Julie K. Monda are participants in the TURC (Tulsa Undegraduate Research Challenge) at The University of Tulsa.

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    Keywords:

    strength training; concentric; eccentric

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