Acute hormonal and neuromuscular responses to hypertrophy, strength and power type resistance exercise

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1 Eur J Appl Physiol (2009) 105: DOI /s z ORIGINAL ARTICLE Acute hormonal and neuromuscular responses to hypertrophy, strength and power type resistance exercise Grant O. McCaulley JeVrey M. McBride Prue Cormie Matthew B. Hudson James L. Nuzzo John C. Quindry N. Travis Triplett Accepted: 24 November 2008 / Published online: 9 December 2008 Springer-Verlag 2008 Abstract The purpose of the current study was to determine the acute neuroendocrine response to hypertrophy (H), strength (S), and power (P) type resistance exercise (RE) equated for total volume. Ten male subjects completed three RE protocols and a rest day (R) using a randomized cross-over design. The protocols included (1) H: 4 sets of 10 repetitions in the squat at 75% of 1RM (90 s rest periods); (2) S: 11 sets of three repetitions at 90% of 1RM (5 min rest periods); and (3) P: 8 sets of 6 repetitions of jump squats at 0% of 1RM (3 min rest periods). Total testosterone (T), cortisol (C), and sex hormone binding globulin (SHBG) were determined prior to (PRE), immediately post (IP), 60 min post, 24 h post, and 48 h post exercise bout. Peak force, rate of force development, and muscle activity from the vastus medialis (VM) and biceps femoris (BF) were determined during a maximal isometric squat test. A unique pattern of response was observed in T, C, and SHBG for each RE protocol. The percent change in T, C, and SHBG from PRE to IP was signiwcantly (p 0.05) greater in comparison to the R condition only after the H protocol. The percent of baseline muscle activity of the VM at IP was signiwcantly greater following the H compared to the S protocol. These data indicate that signiwcant acute increases in hormone concentrations are limited to H type protocols independent of the volume of work competed. In addition, it appears the H protocol also elicits a unique pattern of muscle activity as well. RE protocols of varying intensity and rest periods elicit strikingly diverent acute G. O. McCaulley J. M. McBride (&) P. Cormie M. B. Hudson J. L. Nuzzo J. C. Quindry N. Travis Triplett Neuromuscular Laboratory, Department of Health Leisure and Exercise Science, Appalachian State University, Boone, NC 28607, USA mcbridejm@appstate.edu neuroendocrine responses which indicate a unique physiological stimulus. Keywords Introduction Testosterone Cortisol Force The acute responses of both the endocrine and nervous system to hypertrophy (H), strength (S), and power (P) type resistance exercise (RE) have not been dewned within a single investigation. Much research has been conducted on H type RE protocols which incorporate large muscle group (lower body) at intensities of 70 80% of one repetition maximum (1RM), volumes of three sets of repetitions, and rest periods of short duration (60 90 s) (Crewther et al. 2006; Kraemer et al. 1990). However, there is a paucity of research regarding the acute neuroendocrine response to strength type RE, which has included higher intensities (85 90% 1RM), lower volumes (3 5 sets of 3 5 repetitions) and extended rest periods (3 5 min) (Crewther et al. 2006; Kraemer et al. 1995; Willardson and Burkett 2006b). Additionally, little research has investigated the acute neuroendocrine response to power type RE, which has included high velocity total body movements (jump squats) with lower intensity (0 30% 1RM) and signiwcant volumes (3 5 sets of 6 repetitions) and moderate rest periods (3 min) (Cormie et al. 2007; Linnamo et al. 2005). H type RE has been observed to elicit acute increases in testosterone (T), coritsol (C), sex hormone binding globulin (SHBG), and lactate (La) (Kraemer et al. 1990; Kraemer et al. 2002; Kraemer and Ratamess 2005; Linnamo et al. 2005; McCall et al. 1999). Previous literature has advocated RE of increased volume and relatively short rest periods to elicit an acute hormone response and possibly

2 696 Eur J Appl Physiol (2009) 105: muscle hypertrophy (Kraemer et al. 2002). In contrast, S type RE has typically been performed with greater intensity and signiwcantly less volume when compared to H type RE (Kraemer et al. 1990, 1995; Willardson and Burkett 2006b). Therefore, the higher intensity protocols have been observed to be less evective at eliciting an acute hormone response when compared to moderate intensity protocols (Hakkinen and Pakarinen 1993; Smilios et al. 2003). However, the diverences in the volume examined between S and H type RE cannot be ruled out as the critical determinant of the blunted acute hormone response observed following higher intensity RE (Gotshalk et al. 1997; Kraemer et al. 1990; Ratamess et al. 2005). Moreover, many investigations have not controlled for RE volume when attempting to investigate the evects of other protocol variables on the acute hormone response to RE (Goto et al. 2005; Kraemer et al. 1990; Smilios et al. 2003). Data describing the acute hormone response following P type RE (i.e. light loads moved explosively) are limited. In a previous investigation the leg press was used as the power training exercise and non-signiwcant increases in serum concentrations of T, C, and La were observed (Linnamo et al. 2005). The acute changes in the neuromuscular system that selectively optimize chronic adaptation to the nervous system are not known. Previous research has observed that the magnitude and source of such fatigue may vary when diverent contraction type (Babault et al. 2006), intensity (Linnamo et al. 2000), repetition speed (Linnamo et al. 1998), and rest period (Pattersson et al. 1985) are incorporated into the RE protocol design. One source of fatigue can be dewned as peripheral, which has been identiwed as the failure of force generation by the muscle, due to metabolic by-product accumulation and decreased excitation-contraction coupling (Bigland-Ritchie et al. 1986). In contrast, central fatigue is manifested as an attenuation of muscle activity and force output due to a decreased ability of the central nervous system to elicit motor unit activation (MUA) (Babault et al. 2006). Moderate intensity RE performed under vascular occlusion, which may be similar to that of the H type RE, has been observed to elicit strength gains and increase MUA (Moore et al. 2004). Moreover, RE with short rest periods may promote peripheral fatigue and increase strength through muscle morphology and cross sectional area changes (Moore et al. 2004). Acute decreases in muscle activity have been observed in H type RE previously (Bigland-Ritchie et al. 1986). In contrast, S type RE is known to stimulate type II muscle Wbers as well as increase MUA and therefore may optimize the training stimulus to the nervous system (Campos et al. 2002; Sale 1987). Thus it may be theorized that S type RE may result in greater fatigue due to central origins (Hakkinen 1994). The adaptations to P type RE may include preferential recruitment of type II motor units and the appearance of doublet and triplet muscle activation patterns (Van Cutsem et al. 1998) although the acute neural response to P type RE involving large muscle groups is not well documented. The purpose of the current study was to examine the neuroendocrine response to H, S, and P type RE in a volume controlled randomized investigation. This comparison will assist in determining what acute endocrine and nervous system patterns occur as a result of intensity and rest period manipulation. The observed diverences may provide some possible insight into chronic training adaptations as a result. Methods Subjects Ten male subjects of mean (standard deviation) age 21.8 (1.9) years, height (7.0) cm, body mass 92.4 (9.5) kg, body fat 13.2 (4.2)%, 1RM squat (24.9) kg, strength to body mass ratio 1.9 (0.2) were recruited to participate in this investigation. The subjects were chosen due to their experience (minimum of 2 years) with RE and prowciency in the back squat exercise. During the 1RM testing if the subjects were unable to complete the back squat with acceptable form they were excluded from the investigation. The subjects were instructed to refrain from any intense lower body training 24 h prior to testing and between the testing sessions. Subjects completed a diet recall for the day prior to testing and each day during the testing for each protocol. The diet logs were analyzed using (Food Processor SQL ESHA; Salem, OR). The participants were notiwed about the potential risks involved and gave their written informed consent. This study was approved by the Institutional Review Board at Appalachian State University. Testing sessions The subjects completed four experimental lower body RE protocols. The experimental protocols (H, S, P, and control or rest (R)) were completed in a randomized fashion all on separate days (Fig. 1). Following completion of each protocol the subjects then returned to the lab at 24 and 48 h for a follow-up fasted blood sample and a maximum isometric squat test (Fig. 1). One week was allowed between each treatment (H, S, P, and R). Strength testing Baseline strength levels were determined by assessing 1RM for the back squat exercise as previously described by Matuszak et al. (2003). Prior to completing the dynamic squat the subjects were familiarized with the isometric squat test, described below. Only back squats that achieved

3 Eur J Appl Physiol (2009) 105: Randomized Cross-Over Design Hypertrophy 4 sets of 10 75% 1RM (90 sec rest) 1RM squat protocol Strength 11 sets of 3 90% 1RM (5 min rest) Power 8 sets of 6 jump maximum power load (3 minute rest) 24 hours post Fasted BS 0800 MIS 48 hours post Fasted BS 0800 MIS Control day subject quietly rests Fig. 1 A schematic of the experimental design for the study (blood samples (BS), maximum isometric squat (MIS), one repetition maximum in back squat (1RM)) a knee angle of 90 were considered successful attempts. This knee angle was veriwed by the same individual throughout the study using an elastic cord set to a height at a 90 knee angle. Subjects were motivated equally throughout the study by the three spotters used during all maximal attempts. Experimental protocols All testing was performed between 0600 and 0800 to control for diurnal hormone variation (Bird and Tarpenning 2004). The subjects fasted for 12 h and slept for 8 h prior to each morning blood sample and experimental protocol. The H protocol included four sets of 10 repetitions of parallel back squat at 75% of the 1RM, with 90 s rest periods. The S protocol included 11 sets of three repetitions of parallel back squat at 90% of the 1 RM, with 5 min rest periods. The P protocol included eight sets of six jump squats at body mass, with 3 min rest periods. This load was selected because it has been shown to maximize power output in the jump squat (Cormie et al. 2007). The sets, repetition, and intensity schemes were designed to have equated volume but varied intensity. During the testing the subjects were encouraged to squat to a consistent 90 knee angle squat (ensured by elastic cord as explained above) and repetitions were not considered completed if this knee angle was not achieved or spotter assistance was needed to complete the lift. If failure was reached during a set the load was reduced by 5% for the subsequent set. During all back squats and jump squats the subjects were encouraged to move the bar as fast as possible during the concentric phase. Determination of volume The mechanical work performed as a representation of volume during the eccentric and concentric portion of the back squats and jump squats was calculated using techniques previously described (Liu et al. 2006). BrieXy, eccentric and concentric work was determined by integrating the area under the curve of the force-displacement graphs attained during the eccentric and concentric phases of each jump (Liu et al. 2006). Both vertical and horizontal displacement was measured during all back squats and jump squats through the utilization of two linear position transducers (LPT s) (Cormie et al. 2007). The LPT s were mounted anterior and posterior above the subject on a custom built power rack, then attached to the bar which was held across the subject s back during the back squats and jump squats. Combining the known distances between the two LPT s in conjunction with the displacement measurements of both LPT s as a result of barbell movement allowed for the calculation of vertical and horizontal displacement of the barbell. Vertical ground reaction force (Fz) was measured throughout the series of back squats and jump squats by a force plate (AMTI, BP , Watertown, MA). Analog data (two LPT s and force plate) was recorded by a shielded BNC adapter chassis (National Instruments, BNC- 2090, Austin, TX) and an A/D card (National Instruments, NI PCI-6014, Austin, TX) at 1,000 Hz. LabVIEW (National Instruments, Version 7.1, Austin, TX) was used for recording and analyzing the digital data in which speciwcally designed programs were used to extract and determine the mechanical work (Cormie et al. 2007). Hormone testing Blood samples were performed at baseline following 20 min of quiet sitting prior to exercise (PRE), immediately following the experimental protocol (IP), 1 h post (60P), 24 h post (24P), and 48 h (48P) post to determine the acute responses of serum T, C, and SHBG (Fig. 2). Blood was

4 698 Eur J Appl Physiol (2009) 105: Fig. 2 Schedule of blood samples (BS) and maximum isometric squat (MIS) throughout experimental procedures collected in 10-ml serum Vacutainer tubes and then allowed to coagulate. After approximately 15 min the whole blood was centrifuged at 3,000 rpm (5,000 g) for 10 min at room temperature. The serum was then separated from the blood cells and stored at 20 C until analyzed (Raastad et al. 2000). Blood lactate levels were measured by Wnger tip blood samples at the pre, IP, and 60P. Whole blood lactate concentrations were analyzed using a lactate analyzer (Sport Lactate Analyzer 1500, Yellow Springs Instruments, Yellow Springs, OH). Receptors in the target tissues are exposed to the speciwc serum levels of hormone concentrations, therefore hormone concentration were not adjusted due to changes in plasma blood volume (Rubin et al. 2005). Serum samples for the hormone analyses were only thawed once prior to analysis. Serum concentrations of T, C and SHBG were determined in duplicate using enzyme linked immunosorbent assays (ELISA) kits from DRG diagnostics International (Berlin, Germany). The T/ SHBG ratio has been considered the free androgen index (Ratamess et al. 2005) and was determined to account for the change in bioavailability of T. All the assays were carried out as advised by manufacturer s directions. All samples for each subject were assayed in the same assay for each hormone to avoid inter-assay variation (Ahtiainen et al. 2005). The intra-assay coeycients of variation were 5.4, 6.7, and 7.6, respectively. Neuromuscular performance Isometric muscle strength and muscle activity were measured while the subjects performed an isometric squat at PRE, IP, 60P, 24P, 48P to determine the diverences in the neuromuscular responses. The subjects stood on a force platform under the Wxed bar position at a 100 knee angle and exerted maximal evort by pressing into a Wxed bar for 3-seconds. The subjects were encouraged to push as fast and hard as possible during all trials. The subjects performed at least two trials of isometric squat with the highest peak RFD at 200 ms recorded and used for statistical analysis. RFD was determined at 200 ms after initiation of force. Muscle activity from the vastus medialis (VM) of the subject s dominant leg was recorded through the use of EMG during the isometric squat attempts at 1,000 Hz using a telemetry transmitter (eight channel, 12 bit analog to digital converter, Noraxon USA Inc., Scottsdale, AZ). A disposable surface electrode (Noraxon USA Inc., Scottsdale, AZ) with a 2 cm inter-electrode distance and 1 cm circular conductive area was attached to the skin over the belly of each measured muscle, distal to the motor point, and parallel to the direction of muscle Wbers. Positioning of the electrodes was marked in permanent marker throughout the experiment to maintain consistency in electrode placement. The ampliwed myoelectric signal, recorded during the three trials of isometric squat was detected by the receiver-ampliwer (Telemyo 900, gain = 2,000, diverential input impedance = 10 MΩ, bandwidth frequency Hz, common mode rejection ratio = 85 db, Noraxon USA Inc., Scottsdale, AZ) and then sent to an A/D card. LabVIEW was used for recording and analyzing the data. The signal was full wave recti- Wed and Wltered (six pole Butterworth, notch Wlter 60 Hz, band pass Wlter Hz). The integrated value (μv s) was then calculated and averaged over the 3-s isometric contraction (μv). Statistical analysis Standard statistical methods were used to determine means, standard deviations and Pearson product correlation coeycients. DiVerences between and within the experimental protocols were determined using a general linear regression model (SPSS version 13.0) (repeated measures, Bonferoni Post-Hoc). Statistics performed where compared to resting control values. The signiwcance level was set at p 0.05 for this investigation. Results Volume and quality of resistance exercise completed The total volume of work performed in the H, S and P protocols was found to be equivalent (p = 0.99) (Table 1). Intensity (%1RM) was maintained by the subjects throughout the squat and jump squat sets. SigniWcant (p < 0.01) diverences with respects to relative intensity existed between each protocol with S displaying the highest intensity, followed by H and then P type RE (Table 1). The number of repetitions completed throughout the protocols was inversely relative to intensity, with P greater than H and H

5 Eur J Appl Physiol (2009) 105: Table 1 Comparison of the mean (SD) volume of work, intensity, repetitions, and rest period, peak velocity, peak force, peak power, and time/rep completed between the hypertrophy, strength, and power protocols The values are expressed as means (standard deviation) a SigniWcant (p < 0.05) diverence from power b SigniWcant (p < 0.05) diverence from hypertrophy c SigniWcant (p < 0.05) diverence from strength exceeding S. Rest period was maintained throughout the experiment as previously described. Acute hormone response Hypertrophy Strength Power Work (J) (8.5) 84.2 (19.7) 77.0 (22.5) Intensity 72.8 (2.47) a 89.3 (1.36) a,b 0 (0) (% of 1RM) Total repetitions 37 (3) c 33 (0) 48 (0) b Rest period (minutes) Velocity (m/s) 0.83 (0.12) 0.82 (0.04) 3.67 (.09) b,c Force (N) (104.5) a (55.0) a,b (92.2) Power (W) (492.0) (144.3) b (211.7) b,c Time/rep (ms) (311.7) a (214.3) a,b (132.6) The H protocol elicited a signiwcantly (p < 0.05) diverent percent change from pre to IP for all three hormones analyzed (T, C, and SHBG) in comparison with the R condition (Fig. 3a c). No signiwcant diverences at PRE, IP, or 60P were observed in the raw hormone data within or between protocols. The metabolic demands of the RE protocols represented a titrated pattern dictated by the intensity and rest periods. There was a signiwcant within protocol diverence from pre to IP in whole blood lactate concentration during the H and S protocols. Furthermore, a signiwcant diverence in IP lactate values existed between the H protocol and the S, P, and R. Additionally, the IP lactate value for the S protocol was signiwcantly greater than P and R. A noticeable non-signiwcant trend was observed in the T, C and SHBG data; a dose response relationship was observed between metabolic demand of the protocol and percent change of the hormone concentrations from pre to IP (Fig. 3a c). This dose response relationship was also evident in the signiwcant (p < 0.01) correlation between the IP lactate values and the percent change from baseline of SHBG (Fig. 4). Acute neuromuscular response Both the S and H protocols resulted in signiwcant decreases in isometric squat percent of peak force and rate of force development at the IP time point in comparison to the R condition (Fig. 5a, b). The R and P type RE did not result in signiwcant decrements in any variable examined (Fig. 5a c). P type RE actually resulted in an increase in peak force that surpassed the R condition. At 60P all protocols had recovered to baseline force, RFD, and whole blood lactate values. The percent of baseline muscle activity from the VM Fig. 3 Comparison of (a) total serum testosterone concentration; (b) total serum cortisol concentration; (c) total serum steroid hormone binding globulin (SHBG) concentration; and d) whole blood lactate concentration mean (SE) at rest (PRE black bars), immediately post exercise (IP light grey bars), and at an hour following completion of exercise (60P dark grey bars) for each resistance exercise protocol (hypertrophy (H), strength (S), power (P) and rest (R)). The numbers represent the percent change from pre to IP (n =10). # SigniWcant (p < 0.001) diverence from pre value; *signiwcant (p <0.05) diverence from R protocol; $ signiwcant (p <0.05) diverence from P protocol; ^signiwcant (p < 0.05) diverence from S protocol

6 700 Eur J Appl Physiol (2009) 105: Relationship between Lactate and SHBG Lactate (mmol/l) Hypertrophy Strength Power Rest R = p < SHBG (% change from baseline) Fig. 4 The signiwcant (p <0.001; R = 0.521) relationship between the percent change from rest to immediate post (IP) exercise of the serum concentration of steroid hormone binding globulin (SHBG) and the whole blood lactate concentration at IP for the hypertrophy, strength, power and rest protocol signiwcantly (p < 0.05) decreased IP following the S protocol in comparison to the H protocol (Fig. 5c). The muscle activity from the VM was actually slightly above baseline at the IP time point following the H protocol. A nonsigniwcant trend (p = 0.45) in the VM muscle activity-to-isometric peak force ratio was observed IP following the H protocol in comparison the to R condition (4.1 (1.6), 5.7 (1.8) arbitrary units, respectively). Following the exercise bouts, RFD recovered more readily following the H as opposed to the S protocol. This was evident by the recovery pattern of RFD at 24 and 48 h, which was steeper for the H protocol in comparison the S protocol. This diverence in recovery was observed as the signiwcant (p < 0.05) diverence in the percent of RFD at the 24-h time point between the S and the R condition (Fig. 5b). This was the only diverence in any variable at 24P and 48P. Basal hormone response No signiwcant diverences were found at 24P or 48P for any of the tested hormones concentrations, T/C ratio, or free androgen index (Table 2). A trend following the H protocol was noted with increased levels of T, and T/C ratio at 24 h post in comparison to the other protocols. Nutritional results No signiwcant diverences in the macronutrient composition of the diet on the day preceding and the days during testing were observed between the protocols (Table 3). Fig. 5 Comparison of the mean (SE): (a) percent of baseline force values; (b) percent of baseline rate of force development (RFD) values; and (c) percent of baseline average intergraded electromyography (Avg IEMG) muscle activity from the vastus medialis (VM) at immediate post exercise (IP), 60 minutes (60P), 24-h (24P), 48-h (48P) between the hypertrophy (H), strength (S), power (P), and rest (R) conditions during an isometric squat test. *H protocol signiwcantly (p < 0.05) decreased in comparison to R condition. ^S protocol signiwcantly (p < 0.05) decreased in comparison to R condition. # H protocol signiwcantly (p < 0.05) increased in comparison to S Discussion The primary Wndings from this investigation illustrate that intensity and rest period modiwcation inxuence the magnitude of the acute hormone response to volume equated RE. This is the Wrst study to equate the total volume of RE between two or more protocols with varied goals (H, S, P) and observe signiwcant diverences in the acute hormone response elicited. Additionally, both H and S type RE

7 Eur J Appl Physiol (2009) 105: Table 2 The mean (SE) for the basal hormone response at PRE, 24P and 48P post exercise for Testosterone (T), cortisol (C), steroid hormone binding globulin (SHBG), and T/C ratio to the hypertrophy, strength, and power protocols Hypertrophy Strength Power Rest T (nmol l 1 ) PRE (3.27) (2.42) (2.13) (2.60) 24P (2.67) (2.39) (1.75) (2.75) 48P (2.67) (3.06) (1.87) (2.99) C (nmol l 1 ) PRE (24.73) (77.34) (97.80) (87.13) 24P (34.54) (100.45) (71.04) (114.23) 48P (44.20) (95.31) (129.11) (77.74) SHBG (nmol l 1 ) PRE (5.83) (6.15) (5.09) (5.18) 24P (5.17) (5.29) (4.64) (4.60) 48P (5.16) (5.55) (4.66) (4.93) T/C ratio (%) PRE 4.07 (0.76) 4.93 (1.03) 4.75 (0.67) 4.11 (0.64) 24P 5.91 (0.95) 4.14 (0.44) 4.03 (0.39) 4.52 (0.77) 48P 5.64 (0.86) 5.13 (0.99) 4.82 (0.53) 5.37 (813) Table 3 The mean (SD) for total Kcals, percent fat, percent saturated fat, percent protein, and percent carbohydrate consumed during the hypertrophy, strength, power, and rest condition Hypertrophy Strength Power Rest Calories (kcals) (800.0) (754.4) (616.4) (799.0) Fat (%) 29.4 (7.2) 31.9 (6.8) 35.7 (10.6) 33.9 (11.6) Saturated fat (%) 25.6 (8.7) 27.8 (10.6) 31.1 (8.2) 32.1 (8.1) Carbohydrate (%) 54.8 (10.1) 51.7 (12.6) 47.2 (15.8) 49.7 (14.9) Protein (%) 18.7 (4.1) 18.6 (4.9) 18.9 (5.0) 18.4 (4.1) resulted in acute neuromuscular fatigue, although presumably from diverent sources, central versus peripheral. The H protocol resulted in signiwcantly elevated muscle activity in comparison to the S protocol at the IP time point. Furthermore, the rate of recovery of RFD capabilities was noticeably slower following the S in comparison the H possibly indicating greater disruption of nervous system function. Hypertrophy The H protocol was the only condition which elicited a signiwcant increase in T, C, and SHBG in comparison to the R condition (Fig. 3a c). This Wnding is not unexpected and is in agreement with previous literature (Kraemer et al. 1987, 1990; McCall et al. 1999; Ratamess et al. 2005). The biochemical mechanisms responsible for the observed increases in blood concentrations of hormones are not fully understood and are beyond the scope of the current paper. However, the signiwcant amount of lactate accumulation during H type RE may decrease blood ph and signiwcantly increase catecholamine levels and is speculated to be a key mechanism responsible for the increased T concentrations (Gordon et al. 1994; Kraemer et al. 1987; Lu et al. 1997). The increased C concentration is indicative of a state of catabolism during H type RE. However, the acute increase in T observed may increase androgen receptor binding and set forth the adaptive process leading to increased protein synthesis and thus muscle hypertrophy (Mayer and Rosen 1977). However, a causative link between the acute increases in T, C, and SHBG to muscle hypertrophy cannot be made based on the current data. The H protocol resulted in signiwcant decreases in peak force and RFD with slight elevations in agonist muscle activity. The diverence in agonist muscle activity observed between the H and S protocol at the IP time point is a novel Wnding and is representative of the diverences that can be elicited by varying the metabolic demand of RE through protocol variable arrangement. The phenomenon of increased muscle activity and decreased force output has been termed neuromuscular ineyciency (Deschenes et al. 2000) and may be indicative of peripheral fatigue (Babault et al. 2006; Bigland-Richie 1981; Bigland-Ritchie et al. 1986). The current data are in agreement with previous studies that have elicited neuromuscular fatigue by using vascular occlusion (Moore et al. 2004; Pierce et al. 2006; Taylor et al. 1997). However, the current investigation was the Wrst to elicit this acute evect with structural lower body

8 702 Eur J Appl Physiol (2009) 105: RE in a non-vascular occluded state. Short rest periods may increase motor unit recruitment in spite of attenuated force outputs (Sale 1987); which may explain the increased muscle activity observed following the H protocol. However, this theory is not in agreement with the Henneman et al. (1965) size principle, which states that the majority of larger motor units are not recruited until high relative intensities (90% 1RM) are achieved (Takarada et al. 2000). Recent EMG data have displayed that motor unit recruitment may be optimized without the use of near maximal loading when neuromuscular ineyciency is induced by using vascular occlusion (Pierce et al. 2006; Moore et al. 2004; Takarada et al. 2000). The current Wndings illustrate that neuromuscular ineyciency may be achieved with traditional RE of moderate volume without the use the vascular occlusion. However, conclusions regarding this data should be made with caution; in that neuromuscular ineyciency was not induced by the H protocol in comparison to the rest condition (p =0.45). Strength Previous studies have examined signiwcantly lower volumes of RE when comparing S to H type RE (Crewther et al. 2006; Hakkinen and Pakarinen 1993; Kraemer et al. 1990; Raastad et al. 2000). During RE that incorporates higher intensities (90% of 1RM), as in the S protocol, the volume of RE completed may fall under the threshold necessary to elicit an acute hormone response (Kraemer et al. 1990; Ratamess et al. 2005). However, when performed with substantial volume, high intensity RE was observed to result in a blunted acute hormone response in comparison to the H protocol. This is a novel Wnding and reinforces the importance of manipulating the rest period length and intensity of RE when an acute increase in T is desired. The current data are in agreement with previous Wndings, in which a signiwcant hormone response was not elicited by the higher intensity RE (i.e. S protocols) (Crewther et al. 2006; Hakkinen and Pakarinen 1993; Kraemer et al. 1990). During higher intensity RE a longer rest period length is used to allow for recovery and to maintain volume during the training sets (Willardson and Burkett 2006a, b; Willardson and Burkett 2005). However, the extended rest period length appears to attenuate the magnitude of acute hormone response following S type RE. The S protocol resulted in decreased neuromuscular performance which was evident in the decreased peak force, RFD and muscle activity. There were no diverences in the degree of decline in both peak force and RFD between the H and S protocol. However, the agonist muscle activity following the S protocol was signiwcantly decreased in comparison to the H protocol. The observed decreases in muscle activity following the S protocol were expected and are in agreement with previous literature (Ahtiainen et al. 2003; Hakkinen 1995; Hakkinen 1994). Due to the 5 min rest periods used during the S protocol, whole blood lactate concentrations remained signiwcantly lower than that of the H protocol. This may have accounted for the diverence in muscle activity observed immediately following exercise between the S and H protocols. However, the decreased muscle fatigue does not reveal the cause of the reduction in peak force and RFD observed following the S protocol. The source of fatigue following the S protocol is speculated to be associated with central activation failure which results in decreased muscle activity and force production (Bigland- Richie 1981). The use of higher intensity loading in the S protocol may optimize the stimulus to the nervous system and result in central fatigue. Following the S protocol RFD was signiwcantly lower than the R condition at 24P. The Wnding that high intensity training of suycient volume may decrease RFD in the acute sense is in agreement with Chiu et al. (2004) and Hakkinen (1994). However, a novel Wnding exists in that RFD was decreased at 24P following the S protocol and the recovery pattern of the S protocol was notably slower than that of the H protocol. Power The current data are in agreement with the few studies that have found a negligible hormone response to P type RE (Linnamo et al. 2005). This investigation used zero external loading which may have negatively inxuenced the acute hormone response. Investigations of power training at higher relative intensities may elicit greater magnitudes of hormone response (Crewther et al. 2006). Furthermore, investigations of varied intensities are needed to describe the acute hormone response to the spectrum of P type RE used in practice. However, hormone status following P type RE may not be a critical mechanism related to chronic adaptations following P training. The neural adaptations to P type RE are in contrast to tradition high intensity RE (Sale 1988), and the recommendations for volume and intensity of P type RE are largely unknown. The current study found no acute manifestation of fatigue following a signiwcant volume of jump squats (eight sets of six repetitions). A non-signiwcant trend was noticed as peak force at 60P, 24P and 48P following the P protocol surpassed the R condition. This Wnding is in agreement with Linnamo et al. (2000), in which explosive type lower body RE potentiated multiple aspects of performance. However, the isometric squat may not be a suitable outcome measure to detect fatigue following P type RE. A velocity speciwc test (CMJ, isokenitic dynamometer) may increase the resolution needed to detect changes in the kinetic and kinematic variables following an acute bout of P type RE. Furthermore, the speciwc volume and frequency of P type RE needed to elicit positive neural adaptation is

9 Eur J Appl Physiol (2009) 105: unknown and further research into the acute changes associated with P type RE is needed. In summary, the total volume of RE completed is not the critical variable in eliciting the acute hormone response and may only represent a minimum threshold to be achieved. There is a consensus in the literature that moderate intensity RE of signiwcant volume with short rest periods induces lactate accumulation and increased blood hormone concentrations following RE (Crewther et al. 2006; Kraemer and Ratamess 2005; Kraemer et al. 2002). However, the impact of repeatedly elevated hormone status following extended resistance training on chronic adaptations (i.e. strength expression, muscle hypertrophy) is not known. Future evorts should be made to understand the link between the acute hormone response and the chronic adaptations to muscle elicited by diverent variations of RE. This representation of the acute milieu following volume equated RE may prove to be an evective model for future longitudinal investigations. The data implicate that traditional H type RE may create an internal muscular environment which is similar to that of the vascular occlusion model and may optimize motor unit recruitment to that of high intensity RE. Furthermore, manipulating intensity and rest period can either increase the metabolic or neural demand of the RE. This diverence in RE protocols may lead to a diverentiated source of fatigue (peripheral or central). However, a causative link to the source of fatigue is outside the scope of the current investigation and further study is required. The acute neuromuscular responses to H, S, and P type RE are varied and illustrate the diverent adaptations that can be achieved when chronic training occurs. These data have direct implications to the prescription of RE which should be developed according to the speciwc goal of training. References Ahtiainen JP, Pakarinen A, Kraemer WJ, Hakkinen K (2003) Acute hormonal and neuromuscular responses and recovery to forced vs. maximum repetitions multiple resistance exercises. Int J Sports Med 24: doi: /s Ahtiainen JP, Pakarinen A, Alen M, Kraemer WJ, Hakkinen K (2005) Short versus long rest periods between the sets in hypertrophic resistance training: inxuence on muscle strength, size, and hormonal adaptations in trained men. J Strength Cond Res 19: doi: / Babault N, Desbrosses K, Fabre MS, Michaut A, Pousson M (2006) Neuromuscular fatigue development during maximal concentric and isometric knee extensions. J Appl Physiol 100: doi: /japplphysiol Bigland-Richie B (1981) EMG/force relations and fatigue of human voluntary contractions. Exerc Sport Sci Rev 9: doi: / Bigland-Ritchie B, Furbush F, Woods JJ (1986) Fatigue of intermittent submaximal voluntary contractions: central and peripheral factors. J Appl Physiol 61: Bird SP, Tarpenning KM (2004) InXuence of circadian time structure on acute hormonal responses to a single bout of heavy resistance exercise in weight trained men. Chronobiol Int 21: doi: /cbi Campos GE, Luecke TJ, Wendeln HK, Toma K, Hagerman FC, Murray TF, Ragg KE, Ratamess NA, Kraemer WJ, Staron RS (2002) Muscular adaptations in response to three diverent resistance-training regimens: speciwcity of repetition maximum training zones. Eur J Appl Physiol 88: doi: / s Chiu L, Fry A, Schilling AB, Johnson B, Weiss E (2004) Neuromuscular fatigue and potentiation following two successive high intensity resistance exercise sessions. Eur J Appl Physiol 92: doi: /s z Cormie P, McCaulley GO, Triplett NT, McBride JM (2007) Optimal loading for maximal power output during lower-body resistance exercises. Med Sci Sports Exerc 39: doi: / 01.mss bf Crewther B, Keogh J, Cronin J, Cook C (2006) Possible stimuli for strength and power adaptation: acute hormonal responses. Sports Med 36: doi: / Deschenes MR, Brewer RE, Bush JA, McCoy RW, Volek JS, Kraemer WJ (2000) Neuromuscular disturbances outlast other symptoms of exercise-induced muscle damage. J Neurosci 174:92 99 Gordon SE, Kraemer WJ, Vos NH, Lynch JM, Knuttgen HG (1994) EVect of acid-base balance on the growth hormone response to acute high-intensity cycle exercise. J Appl Physiol 76: Goto K, Ishii N, Kizuka T, Takamatsu K (2005) The impact of metabolic stress on hormonal responses and muscular adaptations. Med Sci Sports Exerc 37: doi: / Gotshalk LA, Loehel CC, Nindl BC, Putukian M, Sebastianelli WJ, Newton RU, Hakkinen K, Kraemer WJ (1997) Hormonal responses of multi-set versus single-set heavy-resistance exercise protocols. Can J Appl Physiol 22: Hakkinen K (1994) Neuromuscular fatigue in males and females during strenuous heavy resistance loading. Electromyogr Clin Neurophysiol 34: Hakkinen K (1995) Neuromuscular fatigue and recovery in women at diverent ages during heavy resistance loading. Electromyogr Clin Neurophysiol 35: Hakkinen K, Pakarinen A (1993) Acute hormonal responses to two diverent fatiguing heavy-resistance protocols in male athletes. J Appl Physiol 74: Henneman E, Somjen G, Carpenter DO (1965) Excitability and inhabitability of motoneurons of diverent sizes. J Neurophysiol 28: Kraemer WJ, Ratamess NA (2005) Hormonal responses and adaptations to resistance exercise and training. Sports Med 35: doi: / Kraemer WJ, Noble BJ, Clark MJ, Culver BW (1987) Physiologic responses to heavy-resistance exercise with very short rest periods. Int J Sports Med 8: doi: /s Kraemer WJ, Marchitelli L, Scott GE, Harman E, Dziados JE, Mello R, Frykman P, McCurry D, Fleck S (1990) Hormonal and growth factor responses to heavy resistance exercise protocols. J Appl Physiol 69: Kraemer WJ, Gordon JF, Gordon SE, Harmon EA, Deschenes MR, Reynolds K, Newton RU, Triplett NT, Dziados JE (1995) Compatibility of high-intensity strength and endurance training on hormonal and skeletal muscle adaptations. J Appl Physiol 78: Kraemer WJ, Adams K, Cafarelli E, Dudley GA, Dooly C, Feigenbaum MS, Fleck SJ, Franklin B, Fry AC, HoVman JR, Newton RU, Potteiger J, Stone MH, Ratamess NA, Triplett- McBride T (2002) American college of sports medicine position

10 704 Eur J Appl Physiol (2009) 105: stand: progression models in resistance training for healthy adults. Med Sci Sports Exerc 34: doi: / Linnamo V, Hakkinen K, Komi PV (1998) Neuromuscular fatigue and recovery in maximal compared to explosive strength loading. Eur J Appl Physiol Occup Physiol 77: doi: / s Linnamo V, Newton RU, Hakkinen K, Komi PV, Davie A, McGuigan M, Triplett-McBride T (2000) Neuromuscular responses to explosive and heavy resistance loading. J Electomyogr Kin 10: doi: /s (00) Linnamo V, Pakarinen A, Komi PV, Kraemer WJ, Hakkinen K (2005) Acute hormonal responses to submaximal and maximal heavy resistance and explosive exercises in men and women. J Strength Cond Res 19: doi: /r Liu Y, Peng CH, Wei SH, Chi JC, Tsai FR, Chen JY (2006) Active leg stivness and energy stored in the muscles during maximal counter movement jump in the aged. J Electromyogr Kinesiol 16: doi: /j.jelekin Lu S, Lau CP, Tung YF, Huang SW, Chen YH, Shih HC, Tsai SC, Lu CC, Wang SW, Chen JJ, Chien CH, Wang PS (1997) Lactate and the evects of exercise on testosterone secretion: evidence for the involvement of a camp-mediated mechanism. Med Sci Sports Exerc 29: doi: / Matuszak MA, Weiss L, Ireland T, McKnight M (2003) EVect of rest interval length on repeated 1 repetition maximum back squats. J Strength Cond Res 17: doi: / (2003) 017<;0634:EORILO>;2.0.CO;2 Mayer M, Rosen F (1977) Interaction of glucocorticoids and androgens with skeletal muscle. Metabolism 26: doi: / (77) McCall GE, Byrnes WC, Fleck SJ, Dickinson A, Kraemer WJ (1999) Acute and chronic hormonal responses to resistance training designed to promote muscle hypertrophy. Can J Appl Physiol 24: Moore DR, Burgomaster KA, SchoWeld LM, Gibala MJ, Sale DG, Phillips SM (2004) Neuromuscular adaptations in human muscle following low intensity resistance training with vascular occlusion. Eur J Appl Physiol 92: doi: /s y Pattersson R, Pearson J, Fisher S (1985) Work-rest periods: their evects on normal physiologic response to isometric and dynamic work. Arch Phys Med Rehabil 66: doi: / (85) Pierce JR, Clark BC, Ploutz-Snyder LL, Kanaley JA (2006) Growth hormone and muscle function responses to skeletal muscle ischemia. J Appl Physiol 101: doi: /japplphysiol Raastad T, Bjoro T, Hallen J (2000) Hormonal responses to high and moderate-intensity strength exercise. Eur J Appl Physiol 82: doi: /s Ratamess NA, Kraemer WJ, Volek JS, Maresh CM, VanHeest JL, Sharman MJ, Rubin MR, French DN, Vescovi JD, Silvestre R, HatWeld DL, Fleck SJ, Deschenes MR (2005) Androgen receptor content following heavy resistance exercise in men. J Steroid Biochem Mol Biol 93: doi: /j.jsbmb Rubin MR, Kraemer WJ, Maresh CM, Volek JS, Ratamess NA, Vanheest JL, Silvestre R, French DN, Sharman MJ, Judelson DA, Gomez AL, Vescovi JD, Hymer WC (2005) High-aYnity growth hormone binding protein and acute heavy resistance exercise. Med Sci Sports Exerc 37: doi: /01.mss C0 Sale DG (1987) InXuence of exercise and training on motor unit activation. Exerc Sport Sci Rev 15: doi: / Sale DG (1988) Neural adaptation to resistance training. Med Sci Sports Exerc 20:S135 S145. doi: / Smilios I, Pilianidis T, Karamouzis M, Tokmakidis SP (2003) Hormonal responses after various resistance exercise protocols. Med Sci Sports Exerc 35: doi: /01.mss F Takarada Y, Takazawa H, Sato Y, Takebayashi S, Tanaka Y, Ishii N (2000) EVects of resistance exercise combined with moderate vascular occlusion on muscular functions in humans. J Appl Physiol 88: Taylor AD, Bronks R, Smith P, Humphries B (1997) Myoelectrical evidence of peripheral muscle fatigue during exercise in severe hypoxia: some references to m: vastus lateralis myosin heavy chain composition. Eur J Appl Physiol 75: doi: / s Van Cutsem M, Duchateau J, Hainaut K (1998) Changes in single motor unit behavior contribute to the increase in contraction speed after dynamic training in humans. J Physiol 513: doi: /j by.x Willardson JM, Burkett LN (2005) A comparison of 3 diverent rest intervals on the exercise volume completed during a workout. J Strength Cond Res 19: doi: /r Willardson JM, Burkett LN (2006a) The evect of rest interval length on bench press performance with heavy vs. light loads. J Strength Cond Res 20: doi: /r Willardson JM, Burkett LN (2006b) The evect of rest interval length on the sustainability of squat and bench press repetitions. J Strength Cond Res 20: doi: /r