Resistance Circuit Training

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Resistance Circuit Training: Its Application for the Adult Population Mike Waller, MA, CSCS*D, NSCA-CPT*D,1 Jason Miller, MS, CSCS,2 and James Hannon, PhD, CSCS1 1Department of Exercise and Sports Science, University of Utah, Salt Lake City, Utah; and 2Department of Human Movement and Exercise Science, Sacred Heart University, Trumbull, Connecticut

SUMMARY session duration, and length of training the physiological markers of health, phase will vary depending on the and (d) strength and flexibility THE PURPOSE OF THE ARTICLE IS training objective. Circuits can be used (5,9,10,18,20,21,25,31). TO FOCUS ON RESISTANCE for health or performance gains with CIRCUIT TRAINING (RCT) AS A each one dictating the aforementioned METHOD OF STRENGTH TRAINING MAXIMUM OXYGEN components (6,19). CONSUMPTION FOR THE ADULT POPULATION. A positive physiological adaptation HEALTH-FITNESS ADAPTATIONS Health-fitness adaptations gained from RCT include improved time to lactate associated with RCT involves changes GAINED FROM RCT INCLUDE _ threshold, increased strength endur- to VO2max. Oxygen consumption is an IMPROVED V_ O max (MAXIMAL 2 ance, and changes in circulating cho- important cardiovascular health pa- AMOUNT OF OXYGEN CONSUMP- lesterol and hormone concentrations rameter and one measurement of TION OF THE BODY DURING EX- (18,31). The current article will not endurance training status. Further- ERCISE) IN CERTAIN CASES, AN focus on all of the health-fitness more, the effectiveness of a training INCREASE IN TIME TO EXHAUS- adaptations because of the length of program to improve cardiovascular TION, A DECREASE IN RESTING the article. However, the initial training health and the efficiency (production BLOOD PRESSURE, INCREASED status, health, and previous exercise of adenosine triphosphate with mini- MUSCULAR STRENGTH, AND experience of an individual will impact mal work) of the aerobic energy system CHANGES IN CIRCULATING CHO- the degree to which these changes can be quantified by increases in _ LESTEROL AND HORMONE CON- occur. Improving health and fitness VO2max (22). CENTRATIONS. RCT MAY USE A through RCT may use a periodized or _ The effects of RCTon VO2max are best PERIODIZED OR PROGRESSIVE progressive program model with the achieved when using a program of PROGRAM MODEL IN A CON- inclusion of plyometrics, explosive lifts, 8–10 stations implemented 3 days per DENSED FORM TO ACHIEVE or high relative intensities in a con- week. This exercise prescription has HEALTH-FITNESS RESULTS BY THE densed form to achieve these results. produced moderate but significant Regardless of the training objective for _ CERTIFIED PERSONAL TRAINER improvements in VO2max in untrained DETAILING LONG-TERM AND RCT, the details of the long-term and postmenopausal women (18.6%), SHORT-TERM PROGRAM PLANS. short-term program plans by a certified college-aged women (10%) and col- personal trainer (CPT) are critical. lege-aged men (11–12%) (5,31). The rest-interval length in those studies that INTRODUCTION PHYSIOLOGICAL RESPONSES TO measured V_ O max before and after CIRCUIT TRAINING 2 lthough many variations or training varied between no rest to 15 descriptions for circuit training The desired physiological responses seconds with work intervals of 30 A exist, this article will focus on that occur as a result of RCT should seconds and intensities of 40–60% of resistance circuit training (RCT) as influence the CPT’s decision on the 1 repetition maximum (1RM). These a method of resistance training that structure of the program. There are intervals can be used as guidelines to uses stations or various exercises per- 4 main physiological areas that have formed with weight training equip- been the primary focus of re- KEY WORDS: ment separated by predetermined rest search conducted on circuit training: _ oxygen consumption; lactate threshold; intervals. The exact number of exer- (a) oxygen consumption (VO2), (b) strength; endurance cises, volume, load, rest-interval length, body composition, (c) changes to

16 VOLUME 33 | NUMBER 1 | FEBRUARY 2011 Copyright Ó National Strength and Conditioning Association progress a program for improving in blood lactate concentrations greater measurements, waist circumference, _ VO2max. than 15 mmol (17). Performing RCT and waist to hip ratio in middle-aged The work to rest ratio is also a critical with short rest intervals may produce individuals and poorly conditioned air factor in prescribing a bout of circuit similar affects on lactate threshold as force personnel (20,30). training for the improvement of aerobic traditional strength training. However, Unfortunately, although there are sig- fitness. For example, an RCT (3 sets 3 the magnitude or significance of the nificant changes in LBM and BF with 8RM 3 3 days) using a rest ratio of 1:2 change in lactate threshold will need to RCT, the lower intensity and lower (30:60 seconds) did not produce im- be quantified in all populations of loads typically used during RCT may provements in cardiovascular variables varying training status. Increases in not impact the bone mineral density (2). However, a multiple set, 8- to 10- lactate threshold may also be possible (BMD) portion of LBM even over station RCT using a work to rest ratio with RCT as a result of the intense 24 weeks of training (5). Although of 1:1 was more effective than tradi- resistance training and short rest peri- improvements in BMD have not been tional strength training in increasing ods. Through RCT, there may be an shown after prolonged RCT, reduc- _ improvement of lactate clearance by an VO2max and may result in increases of tions in BF and increases in LBM are _ increase of mitochondrial density; VO2max upward of 18% (P , 0.01) in positive outcomes from RCT that untrained populations (5). Therefore, though, future research will need to improve physiologic health. a shorter rest period during RCT does investigate the validity of this physio- EFFECTS OF CIRCUIT TRAINING appear to augment improvements in logical adaptation and other possible _ responses. ON PHYSIOLOGICAL MARKERS OF VO2max. However, even with shorter HEALTH rest intervals and lower work to rest BODY COMPOSITION In addition to improvements in health ratios, there are limitations in the An RCT program can affect body com- as a result of changes in body compo- effectiveness of an RCT to increase position in regards to total body mass sition, completing 10 weeks of circuit _ VO2max. A resistance training only (BM), lean BM (LBM), and body fat training performed 3 times per week circuit cannot match the consistent (BF) percentage. Body composition using 50–60% of 1RM can produce aerobic intensity that is accomplished changes will most likely depend on significant increases in high-density through continuous aerobic exercise, the circuit type, with hypertrophy lipoprotein cholesterol (HDL-C) (9). such as running or cycling. Therefore, promoting circuits producing greater Similar increases in acute HDL-C improvements in aerobic capacity as improvements in LBM (15). Studies levels (1 hour after exercise) were a result of RCT will be limited to with rest intervals #1 minute have all quantified after 1 bout of 3 set 10- individuals who have lower pretraining seen significant improvements in body station circuits using a work to rest _ VO2max values. composition whether using moderate ratio 30:30 seconds and similar exercise loads around 70–75% (15,17) or lighter intensity (18). Decreases in low-density LACTATE loads as low as 40–55% (31). The lipoprotein cholesterol and the total Aerobic exercise can be identified by physiological responses leading to cholesterol to HDL-C ratio have also repetitive and cyclic actions, but if these muscle hypertrophy and increases in been seen in paraplegic individuals actions are performed at a higher in- LBM could be a product of higher using an aerobic strength circuit and _ tensity (.75% VO2max), an accumula- training volumes (21). Additionally, in progressive overload scheme (24). tion of lactate in blood and muscles may women, as in traditional strength There is also a benefit after 10 weeks result. The point at which this lactate training, high-volume multiple set cir- of 3 circuits per day using 50–60% of accumulation outpaces disposal is cuits can elicit greater muscle strength 1RM demonstrating an increase in known as lactate threshold, which can when compared with a single-set lower glucose disposal (9). Potential increases eventually lead to temporary cessation volume circuit (21). in glucose disposal may indicate that of muscular contraction. Ability to BF is also positively altered by RCT an RCT is a good exercise mode to change the point of threshold can with Marx et al. (21) showing a BF control type II diabetes (8) and help influence performance by improving reduction in untrained women with control lipoproteins (23). the time to volition of an activity. only 1 circuit session performed 3 Additionally, improved vascular func- Lactate threshold can be a marker of times per week. The traditional 3 days tion (e.g., increased blood flow) has physical performance, although the per week, three 10-station circuits per been seen as a result of circuit training effects of RCT on the time to lactate day using intensities of 40–55% of using loads of around 60% of 1RM but threshold remain unclear. Indications 1RM, and a work to rest ratio of only in individuals who had impaired that lactate levels can be acutely 30:15 seconds also produced signifi- blood flow (10) such as patients with elevated during an RCT session to cant reductions in BF in women (31). coronary heart failure (14). There is concentrations similar to traditional Furthermore, combined aerobic and data suggesting a positive health ben- strength training have been seen after strength exercises in a circuit program efit from RCTon resting and exercising a circuit training protocol that resulted has also shown a reduction in skinfold blood pressure both acutely and

Strength and Conditioning Journal | www.nsca-lift.org 17 Circuit Training

chronically (20,28). Most of the evi- training in individuals who were slightly rate (VE) during RCT (4,12). Consider dence supports a moderate reduction trained (,1 year of training) (15). It that after a period of inactivity from of resting systolic and predominately should be understood that these results surgery, injury, or illness, there can be diastolic blood pressure using an RCT do not suggest a wholesale acceptance of a lowering in respiratory function. at an intensity of 40% of 1RM (20). RCT for developing strength, but it may These limitations experienced by the Although there is no overwhelming be an effective approach to enhancing individual could manifest from a re- evidence for the benefits of RCT on strength in the individuals new to duction in mitochondrial density, im- markers of health, it does appear that strength training. paired vascular system, reduced evidence exists suggesting similar ben- Although when compared with tradi- hemoglobin, or loss of muscle strength, efits from RCT as seen with strength tional strength training, even with mul- preventing higher demanding activi- training. Circuit training could serve tiple sets, circuit training does not yield ties. If the individual is unable to walk as an effective mode to positively similar changes in strength (5) most or ride a bike for a prolonged period influence metabolic variables (choles- likely because of the lower load (#60% (approximately 30 minutes), then an terol and blood glucose), blood flow, of 1RM). The difference between RCT RCT could provide a balance between and blood pressure. A single session of and traditional strength programs in brief bouts of work and rest. The work RCT provides a complete body work- developing strength appears to be pri- to rest ratio then can be changed out while using low intensities and marily because of the lower load not because physical improvements occur requiring a shorter total workout time capable of generating enough stimula- that could lead to incorporation of (around 20–30 minutes) tion for greater muscle recruitment even prolonged aerobic activity or increased after 24 weeks of training (5). RCTduration. One RCT programming point that has been demonstrated in IMPROVEMENTS IN STRENGTH trained individuals is a drop in volume The focus of RCT can be maximal RESISTANCE CIRCUIT TRAINING TARGET POPULATION and load may not be needed with strength, strength endurance, muscle shorter rest periods (1), which is hypertrophy, increased connective tis- Therefore, the use of RCT is limited in the athletic population when strength important as an untrained adult gains sue strength, and improved intermus- experience. These results should be cular coordination (3). Using loading gains are of primary importance. Although limited in use in the athletic encouraging for the CPT who has percentages as low as 40–60% of 1RM limited training time with their clients. during RCT has been shown to population, the use of RCT in a special improve both lower-body and upper- or the general population, where low- APPLICATION body maximum strength in untrained intensity loading still produces gains Studies investigating the effects of RCT men and women (10,31). However, in strength, gives CPTs a valuable have focused on the health benefits application of this load (40–60% 1RM) training method. and the general population. Applying to a trained population may prove less The inclusion of RCT is already the available RCT research along with effective for developing maximal a method of training in cardiac rehab established strength and conditioning strength, so the RCT should use loads setting (14) because of the reduced principles will be used to form guidelines greater than 75% 1RM to improve stress on the heart (30) even when for program development. As previous maximal strength. compared with aerobic exercise (12). literature suggests, rest is an important Even if cardiovascular exercise is in- Improved strength has been observed component to the overall program cluded in the RCT program, strength in RCT program when using intensi- because it can influence adaptation, gains are still seen in untrained or poorly ties around 40% of 1RM, although adherence,andrecovery(3,11,30).There trained individuals (20,29). Additionally, there is also the perception of im- is no standardized work to rest ratio lighterloads(,60%of1RM)usedduring proved functional strength within the but rather guidelines that can be useful only1circuitperformed3timesperweek same rehabilitation population (27,28). when accompanied by some common has been shown to improve muscular These lower strength training intensi- sense. Manipulation of the rest interval strength and, to a lesser extent, muscular ties allow for strength gains for decon- or work by increasing or decreasing power in untrained and poorly trained ditioned muscles, while preventing either of these variables that will subjects (15,21,29). Also, sedentary men major increases in delayed onset typically be indirect of one another participating in a 10-station RCT, for 10 muscle soreness and lower levels of with volume (time exercising) high weeks, displayed a significant 15–42% perceived exertion, which is important and the rest time lowered. A key point increase in strength in pre- to postper- for exercise adherence and safety here is to provide adequate time for rest formance values (13). Interestingly, 1 in the rehabilitation (27) or untrained between exercises, which may be longer circuit was sufficient to increase maxi- adult population. or shorter based on an individual’s mumstrengthandmuscleendurancebut There may also be an improvement to response or adaptation to RCT. not isometric strength when compared respiratory muscle strength and func- Also, changes to the work to rest ratio with multiple circuits over 13 weeks of tion based on the higher ventilation may also be based on the ability of

18 VOLUME 33 | NUMBER 1 | FEBRUARY 2011 a person to complete all repetitions without a concurrent linear increase of exercises that require the greatest duringtheworkphasegivenanyincrease in aerobic work (17). A suggested amount of mental concentration or to resistance/load. The previous para- alternative option to measuring RCT force production would best be placed graph provides an example, although intensity is some sort of rating of at the start of a circuit bout as to individual adaptations should not be perceived exertion scale (12), which minimize the affect of fatigue. Desired overlooked by rigidly following a pro- has been previously used with traditional adaptations of hypertrophy, strength, gram design. There are limitations to resistance training (7). or power from RCT program should using a percentage of maximum heart aid in developing exercise order to rate as a measure of aerobic intensity Successful completion of an RCT pro- invoke the maximal response (11). during RCT because of the error in the gram is also dependent on exercise Random exercise placement during age-predicted formula (.10 bpm) (25) order, which can also influence pro- an RCT session, although a novel andmorespecificallytheexercisepressor gram cessation or adherence. Alternat- approach, has fundamental flaws of reflex (26). The activation of the exercise ing from a lower to upper body, undesirable fatigue increase, potential pressor reflex will result in changes in multijoint to single-joint exercises, or decreases in power production, in- heart rate characterized by large peaks difficult to an easily executed exercise crease of injury risk, and possibly the and valleys during rest intervals (16) are presented (Tables 1, 2). Placement minimization of desired adaptations.

Table 1 RCT for the goal of enhancing overall health in a beginning participant

Work:rest (s)

Exercise station Wk 1 Wk 2 Wk 3 Wk 4 Wk 5 Chest Press 20:30; used for 20:25–20; used for 30:30; used for 30:25–20; used for 30:20–15; used for all exercises all exercises all exercises all exercises all exercises Dumbbell Squats Lat pull-down SLDL Upright cycle Back row Upright cycle Shoulder press Leg press Recumbent cycle Dumbbell biceps curl Recumbent cycle Leg extensions Recumbent cycle Triceps elbow extensions Recumbent cycle Leg curl Upright cycle Abdominal crunch Back extension

The circuit can be repeated more times as the person adapts to the training. Load used should be above the person’s 12RM.

SLDL = Straight leg deadlift.

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In a health-focused RCT, the individual should strive for a greater work and shorter rest interval to maintain a _ higher percentage of VO2 and higher exercising heart rate. By achieving _ a higher mean percentage VO2max and mean heart rate during exercise, possible improvement in HDL-C, intensity for remaining exercises lower total cholesterol, decreased rest- Same volume and ing systolic and diastolic blood pressure, and a reduction in BF percent can be obtained (20,22,23,28). The exact exercises selected for the circuit may have an impact on health adaptations but are dependent on the individual’s initial evaluation and

should be safe to perform. The precise intensity for remaining exercises number of stations are subjective, Same volume and which should be adjusted accordingly to the individual’s ability, time allotted for the session, and the potential of improving the chance of desired adaptations. Incorporating a cardiovascular exercise at a low intensity (,65% _ VO2max) can aid in lactate removal and decrease blood acidosis resulting Rep goal:rest from the resistance training bouts (24). intensity for remaining exercises Same volume and Table 1 presents an RCT for health improvements in a novice adult trainer. Table 2 There will be some strength increases from the program, but the overlying goal is improved health and not maximal strength performance. An RCT used to maximize training time yet develop maximal strength in the adult population would beneﬁt if using an undulating intensity for remaining exercises guide to provide overload and unloading Same volume and sessions over a training cycle. The factors that can be undulated during each session are load, repetition goal, or percent intensity. To insure that rest

time is enough for full recovery of RCT with the goal of enhancing strength in intermediate-level weight trainers or less

a previously exercised muscle group, Wk 1 Wk 2 Wk 3 Wk 4 Wk 5 alternating between upper and lower body is recommended, and by using intensity for remaining exercises

large muscle group/multijoint exercises 12 reps:120 s 12 reps:90 s 15 reps: 90 s 15 reps: 60 s 20 reps:120 s instead of using numerous single-joint medicine ball. ¼ exercises, time can be saved. Table 2 has a list of 8 resistance training stations to be completed during a resistance training circuit focused on Dumbbell; MB

developing maximal strength in an ¼ pullover intermediate trained individual. The The circuit could be repeated for 2–3DB more times as a person adapts. Exercise Clean comboBack squat 6RM:120 s Same volume and 6RM:90 s 3RM:90 s 6RM:60 s 2RM:120 s list in Table 2 may seem short for DB chest press Deadlift 1-arm DB row MB abdominal MB torso rotationGood mornings 12 reps:120 s 10 reps:120 s 12 reps: 90 s 10 reps:90 s 15 reps: 90 s 12 reps: 60 s 15 reps: 60 s 12 reps: 60 s 20 reps:120 s 15 reps:120 s

20 VOLUME 33 | NUMBER 1 | FEBRUARY 2011 a large training group, but adjustments 9. Eirksson J, Tuominen J, Valle T, Sundberg S, Jason Miller is can be made for the best fit to the Sovija¨rvi A, Lindholm H, Tuomilehto J, and an Instructor in individual’s needs and goals following Koivisto V. Aerobic endurance exercise or the Department circuit-type resistance training for specific adaptations to imposed de- of Human Move- individuals with impaired glucose mands or size of the training group ment and Exer- tolerance? Horm Metab Res 30: 37–41, increases. Exercise selection should cise Science at 1998. follow the specificity rule of attempting Sacred Heart 10. Esquivel AAA and Welsch MA. High and to use exercises that will strengthen the University. low volume resistance training and vascular primary muscles used in an individual’s function. Int J Sports Med 28: 217–221, occupation, daily activities, or recrea- 2007. tion sport. RCT may or may not be the James Hannon 11. Fleck SJ and Kraemer WJ. Designing best approach for increasing maximal is an Associate Resistance Training Programs (2nd ed), strength based on the limited research, Professor in the Champaign, IL: Human Kinetics, 1997. pp. but in the time constraints placed on Department of 7–8, 92–102, 228, 232–240. individuals, the circuit approach may Exercise and 12. Green DJ, Watts KW, Maiorana AJ, and O- provide the needed stimulus. Sport Science at Driscoll JG. A comparison of ambulatory the University oxygen consumption during circuit training of Utah. and aerobic exercise in patients with CONCLUSION chronic heart failure. J Cardiopulm Rehabil ThedecisionbyaCPTtousecircuit 21: 167–174, 2001. training programs should be based on the 13. Haber MP, Fry AC, Rubin MR, Smith JC, research, environment, equipment, cli- and Weiss LW. Skeletal muscle and ent’s current training status, and size of REFERENCES hormonal adaptation to circuit weight the class or exercise group. Circuit 1. Alcaraz PE, Sanches-Lorente J, and training in untrained men. Scand J Med Sci Sports 14: 176–185, 2004. training has its value in saving time, but Blazevich AJ. Physical performance and cardiovascular responses to an acute bout like any other program, it does have 14. Hare DL, Ryan TM, Selig SE, Pellizzer A-M, of heavy resistance circuit training versus Wrigley TV, and Krum H. Resistance limitations. Those limitations are found in traditional strength training. J Strength training increases muscle strength, setting the pace (transition time between Cond Res 22: 667–671, 2008. endurance and blood flow in patients with exercises) of the circuit, familiarity of the 2. Allen TE, Byrd RJ, and Smith DP. chronic heart failure. Am J Cardiol 83: selected exercises, the monitoring of the Hemodynamic consequences of circuit 1674–1677, 1999. progression toward training goals, and weight training. Res Q 47: 299–306, 1976. 15. Hass CJ, Garzarella L, De Hoyos D, and remembering that RCT variables may 3. Bompa TO. Periodization Training for Pollock ML. Single versus multiple sets in need to be adjusted every 4–8 weeks to Sports. Champaign, IL: Human Kinetics, long-term recreational weightlifters. Med ensure continued improvements in health 1999. pp. 49–52, 124–130, 191–201. Sci Sports Exerc 32: 235–242, 2000. and performance variables (i.e., strength 4. Braun WA, Hawthorne WE, and Markofski MM. 16. Hempel LS and Wells CL. and aerobic capacity). Even after decades Acute CPTOC response in women to Cardiorespiratory cost of the Nautilus of research, the application and under- circuit training and treadmill exercise of express circuit. Phys Sportsmed 13: 82– standing of where circuit training fits in an matched oxygen consumption. Eur J Appl 97, 1985. effective training program has yet to be Physiol 94: 500–504, 2005. 17. Hurley BF, Seals DR, Ehsani AA, Cartier elucidated. However, circuit training 5. Brentano MA, Cadore EL, Silva EMD, L-J, Dalsky GP, Hagberg JM, and Holloszy holds promise as a viable training method Ambrosini AB, Coertjens M, Petkowicz R, JO. Effects of high-intensity strength training on cardiovascular function. Med for meeting the demands for more time Viero I, and Kruel LFM. Physiological adaptations to strength and circuit training Sci Sports Exerc 16: 483–488, 1984. efficient programs and for introducing in postmenopausal women with bone loss. ¨ ¨ creative and novel training schemes for 18. Jurimae T, Karelson K, Smirnova T, and J Strength Cond Res 22: 1816–1825, Viru A. The effect of a single-circuit weight- those seeking improvements in health. 2008. training session on the blood biochemistry 6. Cassleman R, McFarlane B, McNair L, of untrained university students. Eur J Appl Odgers S, and Thornton KM. Roundtable: Physiol 61: 344–348, 1990. Circuit training. Strength Cond J 12: 16– 19. Kurland HL and Zomar VD. Mike Waller is 27, 1990. Accommodative resistance circuit training a doctoral student 7. Dey ML, McGuigan MR, Bruce G, and for baseball players, Part II. Strength in exercise physiol- Foster C. J Strength Cond Res 18: 353– Cond J 2: 36–40, 1980. ogy at the Univer- 358, 2004. 20. Maiorana A, O’Driscoll G, Dembo L, sity of Utah. 8. Dunstan DW, Puddey IB, Beilin LJ, Burke V, Goodman C, Taylor R, and Green D. Morton AR, and Stanton KG. Effects of Exercise training, vascular function, and a short-term circuit weight training program functional capacity in middle-aged on glycaemic control in NIDDM. Diabetes subjects. Med Sci Sports Exerc 33: 2022– Res Clin Pract 40: 53–61, 1998. 2028, 2001.

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21. Marx JO, Ratamess NA, Nindl BC, 24. Robergs RA, Ghiasvand F, and Parker D. J Cardiopulm Rehabil 8: 292–296, Gotshalk LA, Volek JS, Dohi K, Bush JA, Biochemistry of exercise-induced metabolic 1988. acidosis. Am J Physiol Regul Integr Comp Gomez AL, Mazzetti SA, Fleck SJ, 29. Westcott WL, James JA, Skaggs JM, Physiol 287: R502–R516, 2004. Hakkinen K, Newton RU, and Kraemer WJ. Gibson JR, Reynolds RD, and O’Dell JP. Low-volume circuit versus high-volume 25. Robergs RA and Landwher R. The Comparison of two exercise protocols periodized resistance training in women. surprising history of the ‘‘HRmax=220- on fitness score improvement in Med Sci Sports Exerc 33: 635–643, age’’ equation. JEPonline 5: 1–10, 2002. poorly conditioned air force 2001. 26. Smith SA, Mitchell JH, and Garry MG. The personnel. Percept Mot Skills 104: 22. Mosher PE, Underwood SA, Ferguson MA, mammalian exercise pressor reflex in health 629–636, 2007. and Arnold RO. Effects of 12 weeks of and disease. Exp Physiol 91: 89–102, 2006. 30. Willardson JM. A brief review: Factors aerobic circuit training on aerobic capacity, 27. Sparling PB, Cantwell JD, Dolan CM, and affecting the length of the rest interval muscular strength, and body composition Niederman RK. Strength training in between resistance exercise sets. in college-age women. J Strength Cond a cardiac rehabilitation program: A six J Strength Cond Res 20: 978–984, 2006. Res 8: 144–148, 1994. month follow-up. Arch Phys Med Rehabil 31. Wilmore JHRB, Parr P, Girandola RN, 23. Nash MS, Jacobs PL, Mendez AJ, and 71: 148–152, 1990. Ward PW, Vodak PA, Barstow TJ, Goldberg RB. Circuit resistance training 28. Stewart KJ, Mason M, and Keleman H. Pipes TV, Romero GT, and Leslie P. improves the atherogenic lipid profiles of Three-year participation in circuit weight Physiological alterations consequent to persons with chronic paraplegia. J Spinal training improves muscular strength and circuit weight training. Med Sci Sports Cord Med 24: 1–9, 2001. self-efficacy in cardiac patients. Exerc 10: 79–84, 1978.

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