DTICEffects of different heavy-resistance exercise ELECTE

protocols on plasma #-endorphin concentrations MAR 3 0 1993

CWILLIAM J. KRAEMER, JOSEPH E. DZIADOS, LOUIS J. MARCHITELLI,SCOTT E. GORDON, EVERETT A. HARMAN, ROBERT MELLO, STEVEN J. FLECK,PETER N. FRYKMAN, AND N. TRAVIS TRIPLETTUS Army Research Institute of Environmental Medicine, Natick, Massachusetts 01760-5007;The Center for Sports Medicine, The Pennsylvania State University, University Park, Pennsylvania 16802;and The Sports Science Division, US Olympic Committee, Colorado Springs, Colorado 80909

KRAEMER, WILLIAM J., JOSEPH E. DzLADos, Louis J. MAR- High-intensity maximal exercise may present a physio-CHITELLI, SCOTT E. GORDON, EVERETT A. HARMAN, ROBERT logical involvement of endorphins different from thatMELLO, STEVEN J. FLECK, PETER N. FRYKMAN, AND N. caused by submaximal endurance exercise stress. KjaerTRAvis TRiPLE'r. Effects of different heavy-resistance exercise et al. (22) showed that the depressive effect of epiduralprotocols on plasma (3-endorphin concentrations. J. Appl. Phys- blockade on O-EP concentrations was less pronouncediol. 74(1): 450-459, 1993.-To examine the changes of plasma13-endorphin (3-EP) concentrations in response to various with maximal than with submaximal exercise. It washeavy-resistance exercise protocols, eight healthy male sub- suggested that with maximal exercise, aside from im-jects randomly performed each of six heavy-resistance exercise pulses from the muscles, nervous impulses from the mo-protocols, which consisted of identically ordered exercises care- tor centers in the brain are major determinants of neuro-fully designed to control for the repetition maximum (RM) re- endocrine secretion and enhanced activity in higher neu-sistance (5 vs. 10 RM), rest period length (1 vs. 3 min), and total roendocrine centers. Thus it appears that maximalwork (joules). Plasma #-EP, ammonia, whole blood lactate and short-term exercise presents a neurophysiological exer-serum cortisol, creatine kinase, urea, and creatinine were de- cise stress that is much different from that caused bytermined preexercise, midexercise, immediately postexercise, c ise essutat ch dferen From tt aused)byand at various time points after the exercise session (5 min-48 submaximal endurance exercise. Farrell et al. (13) sug-h), depending on the specific blood variable examined. Only the gested that when an organism is stressed, both the en-high total work-exercise protocol 1 mrin rest, 10 RM load dorphin and the sympathetic nervous systems are acti-(H10/1)] demonstrated significant increases in plasma /-EP ,'ated, and one purpose of the endorphin activation mayand serum cortisol at midexercise and 0, 5, and 15 min postex- be to modulate the amount of sympathoactivation.ercise. Increases in lactate were observed after all protocols, The intensity of the exercise has been demonstrated tobut the largest increases were observed after the H10/1 proto- be a primary variable involved in the stimulatory influ-col. Within the H10/1 protocol, lactate concentrations were ence on plasma #-EP concentrations with exercise (3, 15,correlated (r = 0.82, P < 0.05) with plasma f3-EP concentra-tions. Cortisol increases were significantly correlated (r = 0.84) 19, 20). Still, because of the inverse relationship betweenwith 24-h peak creatine kinase values. The primary finding of exercise intensity and duration of exercise, it appearedthis investigation was that O-EP responds differently to various that a certain duration of exercise would be needed toheavy-resistance exercise protocols. In heavy-resistance exer- stimulate a significant increase in plasma concentrationscise, it appears that the duration of the force production and of fl-EP in a single bout of high-intensity exercise.the length of the rest periods between sets are key exercise Kraemer et al. (28) observed that when exercise intensityvariables that influence increases in plasma ,-EP and serum was increased from 115 to >_175% of maximal 02 con-cortisol concentrations. Furthermore the H10/1 protocol's Sig- sumption (VO2 .. ), significant increases in plasma/f-EPnificant challenge to the acid-base status of the blood, due to sump no segnafic ant ineplasm pr-marked increases in whole blood lactate, may be associated were no longer observed. Heavy-resistance exercise pro-with mechanisms modulating peripheral blood concentrations vides an exercise model for one of the most commonof O-EP and cortisol. forms of high-intensity exercise, which is performed well

above the level that produces V02 .. but uses multi-anaerobic; opioid peptides; creatine kinase; lactate; cortisol; am- ple exercise bouts. Although the duration of exercise ismonia quite short and the intensity very high, multiple bouts of

heavy-resistance exercise using a large amount of totalmuscle mass usually make up a typical exercise session

OVER THE PAST 15 years, endurance exercise has been (23, 27) and may provide the necessary total duration of'Ithe primary focus of research relating exercise stress to exercise needed to stimulate significant increases in

! changes in the peripheral blood concentrations of 6-en- plasma #-EP.Sdorphin (O-EP). It has become evident that higher inten- In a previous investigation, we demonstrated that thep sities of endurance exercise stress produce increases in exercise stimulus used in heavy-resistance exercise can

", plasma concentrations of O-EP both during and after ex- be carefully quantified and related to the configurationSercise (6, 15, 19, 20, 21, 25). of the exercise variables (26). Furthermore it appeared

AD-A262,252 93-06419

ENDORPHINS AND RESISTANCE EXERCISE 451

that the hypothalamic-pituitary axis was very sensitive ing with use of a computer-interlaced load cell and stan-to changes in a heavy-resistance exercise protocol. Our dard body composition methodology (16. 37). Vo.,..previous observations demonstrated that dramatic in- (ml. kg--. min-) was determined utilizing a continuouscreases in serum growth hormone resulted when the du- treadmill protocol (9, 36).ration of the exercise sets (i.e., no. of repetitions) was Experimental design and exercise protocols. Each of theincreased [i.e., rather than using a weight that would al- six heavy- resistance exercise protocols was performed inlow only 5 repetitions, called the 5 repetition maximum random order and by all eight subjects. Subsequent sta-(5 RM), the weight was lightened to allow only 10 repeti- tistical analysis demonstrated no order effects. The de-tions (10 RM)] and rest periods between sets and exer- sign allowed for more quantitative examination of thecises were reduced (from 3 to 1 min) (26). Only in an early effects of specific program design variables (load and reststudy by Elliot et al. (12) were O-EP responses to heavy- period length) corrected for total work. Figure 1 over-resistance exercise examined. Still, the interpretation of views the basic experimental design of the two series ofsignificant increases in plasma O-EP/0-lipotropin after exercise protocols used in the investigation. Two exerciseheavy-resistance exercise remained unclear, inasmuch as series were used in this study, each consisting of threedata from this study were confounded by 0-lipotropin workouts (i.e., a primary workout, a rest control, and across-reactivity and the use of only one resistance exer- load control). The strength (S) series was characterizedcise protocol. Thus it was unclear whether resistance ex- by heavier resistance (i.e., 5 RM) in the primary workout.ercise per se would provide the necessary stimulus for The hypertroI iy (H) series used a lighter resistance (i.e.,increased plasma concentrations of O-EP or whether the 10 RM) in the primary workout but had a higher volumecharacteristics of the exercise protocol utilized were vi- of total work. The S series had significantly (P < 0.05)tal, as previously observed with growth hormone. It was lower total work than the H series (49,980 ±+ 10.473 vs.hypothesized that increases in plasma O-EP concentra- 60,427 ± 13,428 J).tions would follow a pattern similar to growth hormone As in our previous study (26), the primary workout inand be most sensitive to the same long-duration and the S series consisted of a 5-RM load and a 3-min restshort-rest protocol that was used previously and elicited period between sets and exercises. It was designated S5/the greatest response of the hypothalamic-pituitary axis. 3, meaning S for the S series (lower total work), 5 for theTherefore the primary purpose of the present study was 5-RM load, and 3 for the 3-min rest periods. The loadto examine the changes in plasma concentrations of 0- control workout for the S series used a 10-RM load andEP in response to the same quantified array of heavy-re- was designated S10/3. The rest control workout for the Ssistance exercise protocols used previously (26). This series used a 1-min rest period and was designated S5/1.would help extend our understanding of the influence of The same type of terminology was again utilized to desig-exercise variables on peripheral plasma /-EP concentra- nate each exercise protocol in the H series. The primarytions with this type of high-intensity intermittent resis- protocol for the H series was designated H10/1, meaningtance exercise stress. It might also provide the basis for H for H series (higher total work), 10 for the 10-RM load,further investigations into the physiological mechanisms and 1 for the 1-min rest periods between sets and exer-involved with increases in plasma /3-EP with high-inten- cises. Similarly, the load control workout used a 5-RMsity exercise. load and was designated H5/1, and the rest control work-

out used 3-min rest periods and was designated H10/3.

METHODS Although both exercise protocols produce increases instrength and muscle cell hypertrophy, the S5/3 workout

Within the context of our previous investigation (26), is typical of weight-training protocols used primarily foreight of the nine male subjects were utilized in this inves- "strength" development and the H10/1 workout is typi-tigation to examine the plasma /-EP response patterns cal of exercise regimens used by body builders to induceto the same combination of heavy-resistance exercise increases in muscular hypertrophy (27). Thus each exer-protocols used previously. Each subject gave informed cise series provides for specific program differences be-written consent to participate in the investigation. The tween exercise protocols on the basis of the configurationphysical characteristics of the subjects were as follows of the exercise stress variables. The variations of the pri-(means ± SE): age, 24.7 ± 1.6 yr; height, 178.4 ± 2.9 cm; mary workouts were examined to help determinebody mass, 82.1 ± 4.4 kg-, V0o2m,, 55.2 ± 0.8 ml' kg'-' whether differences in responses occurred because ofmin'-; and body fat, 16.1 + 1.6%. All subjects were in single factor changes in load and rest period lengths.good health and had recreational experience with resis- Comparisons between a few S and H series protocolstance training, but none were competitive lifters. The (S10/3 vs. H10/3 and S5/1 vs. H5/1) allowed a limitedsubjects had no history of any endocrine disorders or evaluation of total work effects. The exercises utilized.drug use and were not on any medications or nutritional the order used, and the number of sets for the primarysupplementation during the course of the investigation, workouts can be seen in Table 1. Each of the two exercise

Except for the dependent variables, the times when series had a primary workout (S5/3 and H10/1), a loadblood samples were obtained, and biochemical methodol- control (S10/3 and H5/1), and a rest control (S5/1 andogies, the methods of the study were identical to those 1110/3). All workouts within a series involved the samepreviously described (26). A minimum of 2 wk was taken total work.for experimental protocol familiarization, descriptive The grip width used by each subject was proportionaltesting, and load verification for each exercise protocol. to his height. Body position of all subjects (e.g., gripBody composition was determined by hydrostatic weigh- width, joint angles) was held constant for an exercise in

452 ENDORPHINS AND RESISTANCE EXER('ISE

5 RM, 1 min (S5/1) 5 RM, I min (H5/ )(Series I Rest Control) (Series 2 Load Control)

Decreased Rest Increased Load

I WU(Primary Workout) (Primary Workout)

5 RM, 3 min (S5/3) 10 RM, rmin (HIO/1)

f fDecreased Load Increased Rest

10 RM, 3 min (310/3) 10 RM, 3 min (HlO/3)(Series 1 Load Control) (Series 2 Rest Control)

FIG. 1. Schematic diagram of experimental design. RM, repetition maximum.

all protocols. The matching of total work between work- and estimate body segment weights from total bodyouts was performed by a computer program that, given a weight (38).specific exercise, weight, and number of repetitions, cal- Experimental protocol. One week separated each ran-culated the number of repetitions required to produce domized experimental protocol. Subjects refrained fromthe same total work as in the primary protocol in which a ingestion of alcohol or caffeine for 24 h and did not per-different weight was used. Lifting work was calculated as form any strenuous exercise for 48 h before the experi-weight X vertical distance moved per repetition x num- mental exercise session. Testing with 1 RM every otherber of repetitions. The program took into consideration week demonstrated that no strength changes occurredthe vertical distance moved by both the iron plates and over the course of the study. In addition, aerobic exercisethe centers of gravity of the lifter's body segments. These was limited to two sessions per week, with no trainingdistances were obtained from measurements on the sub- effects observed over the course of the study.jects and equipment when the subjects were in the start- All venous blood samples were obtained with the sub-ing and ending exercise positions. Anthropometric tables jects in a slightly reclined seated position. Testing waswere used to locate body segment centers of gravity always conducted at the same time of day to reduce the

effects of any diurnal variations on hormonal concentra-tions. Before a resting blood sample was obtained, a 20-TABLE 1. Experimental heavy-resistance min equilibration period was utilized. Subjects knew theyexercise protocols would not start exercising until 10 min after the resting

RM and No. of Sets blood sample was obtained. This procedure was shownduring pilot testing to eliminate any significant anticipa-

Series I Series 2 tory increases in hormonal responses, sometimesExercise Order (S5/3) (HI0/1) thought to affect the examination of exercise responses.

11 Bench press 5 RM X 5 sets 10 RM x 3 sets Water intake was allowed ad libitum throughout the ex-2) Double kg extension 5 RM x 5 sets 10 RM X 3 sets ercise protocols and recovery. The venous blood samples3) Military press 5 RM X 3 sets 10 RM x 3 sets were obtained from an indwelling cannula in a superficial4) Bent-leg incline sit-ups 5 RM x 3 sets 10 RM x 3 sets5) Seated rows 5 RM X 3 sets 10 RM Y 3 sets arm vein kept patent with isotonic saline (30 mI/h).6) i•it pulldown 5 RM X 4 sets 10 RM x 3 sets Blood samples were obtained preexercise, midexercise7) Arm curls 5 RM X 3 sets 10 RM x 3 sets (i.e., after 4 exercises), immediately postexercise, and at.8) Leg press 5 RM x 5 sets 10 RM x 3 sets various time points (i.e., 5 min-48 h) after the exercise

All exercises were performed on a Universal weight machine, except session, depending on the specific blood variable exam-exercises 4 and 7, which utilized free weights. RM, repetition maximum. ined. Whole blood was processed, and where appropriate.

ENDORPHINS AND RESISTANCE EXERCISE 453

serum and plasma samples were stored in an ultralow sponses for the various exercise protocols at these timefreezer at -120'C until analyses were performed. Rat- points, indicating dramatic effects in response to chang-ings of perceived exertion (RPE), utilizing the Borg CR- ing the rest period length (i.e., from I to 3 min; or in-10 scale designed to accommodate primarily anaerobic creasing the resistance load (i.e., from I0 to 5 RM). Noexercise, and heart rate via electrocardiogram were ob- differences were observed in total work between the ap-tained immediately after each exercise set (31). propriate S and H series protocols. Furthermore, no dif-

Biochemical analyses. Whole blood lactate concentra- ferences from preexercise values were observed in restingtions were determined in duplicate via a lactate analyzer values 24 and 48 h after the exercise sessions.(model 640, Wolverine Medical, Grand Rapids, MI). He- The acute responses of serum cortisol (Fig. 2B) fol-moglobin was analyzed in triplicate usingthe cyanmethe- lowed a pattern similar to that onserved for 3-EP. Themoglobin method (Sigma Chemical, St. Louis, MO), and H10/1 protocol produced significant increases, whichhematocrit was analyzed in triplicate utilizing a standard were greater than all other exercise protocols at the re-microcapillary technique. The percent change• ir. pirma spcctivv time,,. Similarly, an increase in the rest periodvolume were calculated according to equations by Dill length or the resistance load resulted in marked reduc-and Costill (11). Serum creatine kinase (CK), creatinine, tions in the serum cortisol concentrations. Again, no dif-serum urea, and plasma ammonia were all determined in ferences were observed for appropriate total work corn-duplicate using colorimetric assay methods and a Gilford parisons between the S and H series.Stat Star spectrophotometer (Sigma Chemical). Intra- Lactate and ammonia. Figure 3 shows the responses ofand interassay variances were all <5 and 8%, respec- blood lactate (A) and plasma ammonia (B). Significanttively. Except for hemoglobin, all serum andplasma sam- whole blood lactate increases above resting values werepies were run in duplicate and were decoded only after observed at various times during and after exercise inanalyses were completed (i.e., blinded analyses). For am- each exercise protocol. The magnitude of increase wasmonia and hormonal analyses, blood was collected into again greatest with the 110/1 protocol.prechilled plastic syringes containing EDTA (1.2 mg/ml agi greatest with the / protocol.whole blood), mixed gently, and centrifuged at 1,500 g at The effects of rest period change in the S series showed4'C for 15 min. Plasma determinations of the different that decreasing the rest period to l ma (from $5/3 toimmunoreactivity values were accomplished with the use $5/1) significantly increased the lactate concentrationsof a Beckman 5500 gamma counter and on-line data re- over s5/3 values at midexercise and 0, 5, and 15 manduction system. The plasma O-EP radioimmunoassay postexercise. In the H series, increasing the rest period(RIA) procedure ("25I liquid-phase RIA with prior column from 1 (H10/1) to 3 min (H10/3) significantly decreasedextraction; INCSTAR, Stillwater, MN) is described in lactate values at midexercise and 0, 5, and 15 min postex-detail elsewhere (24). Cross-reactivity with f-lipotropin ercise.was <5%. The interassay variance was 8.1%, and the in- In the S series, a significant reduction at midexercisetra-assay variance was <4.5%. Serum cortisol concentra- was the only difference observed in whole blood lactatetions were assayed utilizing a solid-phase "25I RIA tech- when the load was lightened (from S5/3 to S10/3). Con-nique (Diagnostic Products, Los Angeles, CA). The in- versely, in the H series, when the load was increased fromterassay variance was <6.6%, and the intra-assay 10 to 5 RM (from H10/1 to H5/1), significant decreasesvariance was <4.1%. All hormonal variables were were observed in lactate at midexercise and 0, 5, and 15corrected for plasma volume shifts. min postexercise. Appropriate total work comparisons

Statistical analyses. Statistical evaluation of these data (i.e., S5/1 vs. H5/1 and SO/3 vs. H1O/3) showed no pair-was accomplished utilizing a multivariate analysis ofvari- wise differences in lactate between S5/1 and H5/1, butance with repeated measures. Subsequent post hoc pair- H10/3 values at midexercise and 0, 5, and 15 min postex-wise differences were determined using Tukey tests. ercise were significantly greater than S10/3 values atPearson product-moment correlations were utilized to those time points.examine various bivariate relationships. Dependent t For plasma ammonia (Fig. 3B), no significant in-tests were used for comparisons of the total work of the creases were observed above rest for any of the timetwo series of heavy-resistance exercise protocols. The sig- points examined in the S series protocols (left panel). Innificance level for this study was P < 0.05. the H series, significant increases were observed above

rest for H1O/1 at midexercise and for H10/1 and H5/1

RESULTS immediately and 5 min postexercise. Again, similar tolactate, the magnitude of increase was greatest with the

The most prominent finding in this study was that the H10/1 exercise protocol. Total work comparisons (i.e..H10/1 protocol stimulated the highest magnitude of re- S5/1 vs. H5/1 and S10/3 vs. HI0/3) showed pairwise dif-sponse for most of the variables examined. No significant ferences in ammonia, inasmuch as values for H5/1 weredifferences were observed in resting baseline values be- greater than those for S5/1 immediately, 5 min, and 24 htween exercise protocols for any of the blood variables postexercise. S10/3 ammonia values 24 and 48 h postex-examined. ercise were greater than corresponding concentrations

t3-EP and cortisol. The responses of plasma 3-EP to the for H10/3.various heavy-resistance exercise protocols are shown in In the S series, decreasing the rest period to I minFig. 2A. Significant increases in plasma fl-EP were ob- (S5/3 to S5/1) had no effect on plasma ammonia results.served only for the HI0/1 protocol. These elevations In the H series, increasing the rest period from I (H 11/1)were significantly greater than any of the other re- to3 min (HO/3)significantlydecreased ammonia vaiues

454 ENDORPHINS AND RESISTANCE EXERCISE

AI0 H Ic

30 S30 1 3

S SJ25 25

0.

IS is

* Ix~ .. iT

10 C o

0 0Pro Mid PE S rin 15 tnin 24 hr 48 hr Pie Mid FE 5 ISn en 24 h, 48 h,

B

1000- H000

B~ , n I

S 0W a 00

-mo

SW

E C

40 4WS 00

300 3E00Pre Mid C)5 mnn is i Pro Mid FE 5 min is nvn

FIG. 2. Plasma #-endorphin (A) and cortisol (B) during strength (S, left) and hypertrophy (H) protocols (right).Values are means _± SE. Pre, preexercise; Mid, midexercise; IPE, immediately postexercise. * S~ignificant difference (P< 0,05) from corresponding preexercise values.

at midexercise and immediately and 5 min postexercise. the H series, significant increases above rest were ob-In the S series, no significant changes were observed served for H10/1 and H5/1 120 rain postexercise. Allwhen the resistance load was lightened (from S5/3 to three protocols increased at 24 h, whereas only the H 10/1S10/3). Conversely, in the H series, when the load was and H5/1 values remained elevated at 48 h. At 120 minincreased (from H10/1 to 1-5/1), significant decreases and 24 h postexercise, the H10/1 protocol resulted inwere observed in plasma ammonia concentrations at mid- serum CK concentrations significantly greater than forexercise and immediately and 5 min postexercise. any other heavy- resistance exercise protocol.

Creatinine and urea. No significant changes from rest- Figure 5 shows the response of RPE (A) and heart rateing values or differences between any of the heavy-resis- (B) for the different exercise protocols. Except for antance exercise protocols were observed for either serum increase in RPE for S5/3 immediately after the workout.creatinine (range 200.3 ±_ 15.91 to 350 +_84.86 ttmol/l) or no further significant changes were observed over theserum urea (range 13.5 ± 7.2 to 19.52 +5.8 g/dl) concen- course of each of the exercise protocols. Still, in the Strations measured immediately postexercise and 120 series, RPE for S5/1 was significantly greater than forrain, 24 h, and 48 h after exercise. S5 /3 and H 10 /3 after exercise I and midworkout. Iminmedi -

CK. In Fig. 4 the responses of serum CK are presented. ately after the exercise protocol, RPE for S5/3 and S5/1In the S series, significant increases above rest were ob- were greater than for S10/3. In the H series, RPE forserved after each protocol at 120 min and 24 h, with only H10/1 and 115/1 were greater at all corresponding timethe S5/3 and S5/1 values remaining elevated at 48 h. For points than for H10/3. For total work comparisons, RPE$5/1, CK concentrations were significantly greater at were greater for H10/3 than for S10/3, whereas no signifi-120 min and 24 h than for any of the other S protocols. In cant differences were observed between S5/1 and H5/1.

ENDORPHINS AND RESISTANCE EXERCISE 455

A

10 10

•2

0C0

2 2

PNe Mid IPE 5 -n 15. mn 120 rin 24 h, 48 h, Pe Mid IP0 5Cr 15- 12f)-C ;4'- 4r hN

B-- 0- G 5/3 0 i

[S1013 1

400 S 5/1400

350 350

a 300 a 3000

. 250 '250

0 200 0 200E E

CO 50 CO150

E E

,00 0.100

50 5o

Pro Mid P 5mi 241v 48hr Pre Mid PE 5 min 24 h" 48 h,

FIG. 3. Whole blood lactate (A) and plasma ammonia (B) during S (left) and H protocols (right). Values are means tSE. * Significant difference (P < 0.05) from corresponding preexercise values.

The heart rate responses shown in Fig. 5B demon- various heavy-resistance exercise protocols. When thestrated expected increases after exercises 4 and 8. Only relationship between plasma O-EP and whole blood lac-for H t0/1 did heart rate remain above preexercise values tate responses was examined using all the time pointsfor the entire exercise protocol. from just the H10/1 protocol, a significant correlation

The greatest percent changes in plasma volume were was observed (r = 0.82). Ammonia was correlated toobserved pre- to postexercise and were as follows: S5/3, whole blood lactate in the H10/1 protocol (r = 0.83). CK-6.69 ± 4.28% (SD); S10/3, -3.43 ± 4.15%; and S5/1, concentrations at 24 h were significantly correlated with-4.87 ± 2.46%; H10/1, -8.77 ± 5.42%; H5/1, -3.44 ± the highest serum cortisol concentrations measured 52.64%; and H10/3, -2.87 ± 2.41%. min postexercise when only the data from the H10/1

Simple linear regression analyses among all the de- protocol were examined (r = 0.84).pendent variables were performed for each of the specificindividual heavy-resistance exercise protocols. The first DISCUSSIONstatistical approach utilized all the time points in theanalyses, and the second approach examined the correla- The exact mechanism(s) responsible for exercise-in-tional relationship at each of the specific time points duced increases in O-EP, adrenocorticotropic hormonewithin each exercise protocol. This was done to deter- (ACTH), and cortisol remain speculative and may differmine significant correlations within a specific heavy-re- between submaximal and maximal (i.e., Vo 2 ma) exercisesistance exercise protocol for the dependent variables stressors (18, 22). Furthermore it has been known for ameasured in this investigation. The following are the long time that differences exist between the responses ofonly significant correlations observed within each of the O3-EP in the central nervous system and peripheral circu-

456 ENDORPHINS AND RESISTANCE EXERCISE

A B -.--. M,'350 S 10It3 350 e H idl

SS ---J 0 H 4,3

300 0

250-E E

0 l. 0 5

100 100

Pro 1E 120 min 24 hr 48 hr Pro IP 120 m0n 24 hr 48 h,

FIG. 4. Serum creatine kinase during S (A) and Hf protocols (B). Values are means __SE. * Significant difference(P < 0.05) from corresponding preexercise values.

lation (33). Thus, implications to central mechanisms set durations (as determined by the RM resistance used)with exercise stress remain beyond the scope of this in- and interset rest periods.vestigation, which examined the possible influences on Although the exact mechanisms responsible for exer-the peripheral #3-EP concentrations in the blood. Al- cise-induced increases in plasma O-EP in response tothough short-term anaerobic exercise to exhaustion has high-intensity exercise remain unknown, it has been sug-been shown to increase plasma O-EP and serum cortisol gested by Kjaer et al. (22) that nerve impulses from theconcentrations in the blood, intensities that are very high motor centers in the brain may directly enhance the activ-and of short duration do not appear to elicit a change in ity of higher neuroendocrine centers. In our previousthe peripheral plasma concentrations (28). Little is study with essentially the same subject population,known about responses of plasma O-EP to repetitive and growth hormone also responded markedly to the H10/1very-high-intensity exercise, as characterized by heavy- protocol (26). Yet, unlike growth hormone responses,resistance exercise. plasma fl-EP concentrations responded to only one

The primary finding in the present study was that only heavy- resistance exercise protocol. Thus a general stressone of the six heavy- resistance exercise protocols exam- response to heavy-resistance exercise of the hypotha-ined resulted in a significant increase in plasma O3-EP lamic-pituitary axis does not appear plausible. In addi-and serum cortisol concentrations. In general, these data tion, cortisol demonstrated a similar response patternindicate that specific configurations of heavy-resistance with O3-EP over the first 15 rain Of recovery, and thisexercise programs may differentially influence mecha- response is most likely reflective of ACTH release withnisms that perturb peripheral plasma concentrations of high-intensity exercise, which has been shown to typi-these hormones. Because exercises used in each heavy- cally follow #3-EP responses (25, 28). Cortisol has beenresistance exercise protocol remained identical for each observed to be responsive to short-rest (i.e., 10-60 s)protocol examined, it appears that the exercise stimulus heavy- resistance exercise protocols (27).most effective in causing dramatic increases in plasma In a recent study by Farrell and co-workers (13) exam-$-EP is characterized by longer-duration sets (i.e., 10- ining a number of different stressors, maximal handgripRM load ') and shorter rest periods between sets and exer- exercise produced an exaggerated pressor response whencises. As pointed out by Goldfarb et al. (19), there might opioid actions were blocked by naloxone, thus suggestingbe a threshold of exercise intensity above which plasma that opioid peptide systems may play a role in modulat-O-EP concentration is a function of both the duration ing sympathetic responses. Although the study by Farrelland intensity of exercise. Our data indicate that, with the and co-workers (13) examined much smaller muscletype of high-intensity resistance exercise used in this in- group activity, such data do imply that the sympatheticvestigation, the number of repetitions that the resistance nervous system responses and pressor activity may be(i.e., intensity) allows (e.g., 5 or 10 RM) in the set (i.e., involved with the increases observed in O-EP in responseduration) and interset rest period length are the primary to heavy- resistance exercise. The magnitude of the pres-determinants of physiological stress. The most marked sor response with large muscle group heavy -resistancechanges in the hormonal responses were produced when exercise has been shown to involve marked pressor andthe resistance allowed only 10 RM and when short rest sympathetic nervous system involvement (17, 22, 23, 27,periods were utilized. Our experimental design is limited 30). The combination exercise stress in the H I0/i1 heavy-in describing any intensity/du ration dual threshold. Fur- resistance exercise protocol of longer-duration (10-RM)ther study is needed to establish a continuum of re- sets and shorter rest periods (1 min) allowed less cardio-sponses of plasma #•-EP to heavy- resistance exercise vascular recovery between sets. The use of a 10-RM resis-with use of a combination stress consisting of different tance for each exercise may have maintained a higher

ENDOflPHINS AND RESISTANCE EXERCISE 457

A---- 0-- H 0,2

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12 12

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2 1

B-a-.--- so

to 170

o t•o

S91 90

70- 70

43 3

2 2

After exercise 1 Mr d workou After workout After H rcols ritd.of Vau es Are

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men S.*Sgiicn ifrne( 0.5 frmcorsonigpreerievaus

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co o Cca M C

mean ±/ SE */ Sinfcn difrec (P </ 0.5 frmcrepnigpree aus

Some evidence to support this speculation may be ob- latiopship has never been demonstrated. In this investi-served in the heart rate responses of the subjects, which gation, a significant correlation (r = 0.82) was observedremained significantly elevated above the resting level between plasma O3-EP concentrations and whole bloodfor the entire H10/1 protocol. The longer duration of lactate only with the H10/1 protocol, which demon-each set with resistances of 70 and 80% of the 1 RM have strated the highest blood lactate responses. It is interest-been shown to result in higher arterial blood pressure ing that when the load was increased, the whole bloodresponses than shorter-duration sets using maximal or concentration of lactate was decreased, most likely duenear-maximal (90-100% of the 1-11M) resistances (17). It to the short duration of exercise associated with the 5-remains to be directly demonstrated whether the higher RM set. We did not observe any significant relationshipsplasma O-EP concentrations observed in this study for between Ol-EP and any of the other blood variables suchthe H10/1 protocol are related to such a modulation and as ammonia, urea, or creatinine. It appears that mecha-maintenance in the magnitude of sympathetic excitation nisms related to acid-base status of the blood are in someand pressor responses during the exercise protocol. way associated with changes in plasma O•-EP. Previously,

The influence of "anaerobic factors" as a systemic we demonstrated that increases in lactate alone do notstimulus for increases in proopiomelanocortin (POMC) result in increased plasma O-EP concentrations (28). Sig-peptides in the plasma has been suggested (14, 25). De- nificant correlations with O-EP and lactate have beenspite significant correlational relationships between in- observed primarily for longer-duration (i.e., 5 rain) high-

458 ENDORPHINS AND RESISTANCE EXERCISE

intensity exercise (25). Conversely, with submaximal Address for reprint requests: W. J. Kraemer, Center forSports Medi-

single-bout high-intensity exercise of very short duration cine, 117 Ann Bldg., The Pennsylvania State University. tniversitv

(<3 min), such bivariate relationships between lactate Park, PA 16802.

and O-EP have not been consistently observed (20, 28). Received 15 January 1992; accepted in final form 21 July 1992.Thus, these data, along with the data from previous in-vestigations, start to indicate that the exercise stress may REFERENCES

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