The RT group performed upper- and lower-body RT exercises that consisted of free weights (i.e., barbell and dumbbell), machines, and body weight (Table 2). The resistance machines used were Atlantis Strength Equipment products (Laval, QC, Canada), which allowed for full range of motion, smooth action, and easy pin adjustment of the load. The load (resistance) for each exercise was determined at baseline and week 8 according to the 10RM method. This enabled the establishment of new loads for each exercise to continually stress the bodies of the RT group throughout the study. The baseline 10RM testing session was supervised to teach the subjects proper exercise technique, and how to correctly determine and record their 10RMs for each exercise. The RT sessions were carried out at the University of Regina fitness and lifestyle center. The fitness and lifestyle center had 2 staff members on the workout floor at all times, and the staff were familiarized with the research study and the RT exercises used in the study. A traditional periodized training program was used, consisting of 3 sessions per week, intensity range 53-72% 1RM, with 1-3 minutes of rest between sets and exercises (3). The rest time was dependent on the load (12-15RM = 1 minute of rest on all exercises; ≤10RM = 3 minutes of rest on primary exercises). Primary exercises were leg press, bench press, and incline bench press. In contrast to the other exercises, the prone superman was body weight resistance only. The subjects completed 10 repetitions each set, with pauses ranging from 5 to 30 seconds per repetition. The progressive overload was administered by increasing the duration of the pause (isometric contraction of the erector spinae), which was governed at the discretion of the subject. The RT group subjects were asked to follow the exercise order as defined within the program. All the RT exercises were performed using concentric and eccentric muscle actions in smooth, controlled motions. As previously stated, the prone superman also contained an isometric contraction. This type of periodized RT program has been used in our previous training studies (25,28).
The periodized progressive overload AT program consisted of 3 sessions per week, a Borg scale range of 8-12, session duration of 20-35 minutes, and a total weekly duration of 55-155 minutes (Table 3). The mode of AT exercise consisted of any form of aerobic exercise in which the subject was interested, with the most commonly selected modes being the elliptical trainer and treadmill walking or jogging. The only mode of exercise excluded was swimming, because of the body position's effect on heart rate and the potential influence on the exerciser's rating of perceived exertion (RPE). The option to self-select the mode of AT was provided to increase retention and improve generalizability to the real-world setting. During the laboratory testing session, the subjects were familiarized with the use of the Borg scale for rating perceived exertion. The intent was to use the Borg scale to set the intensity of the AT sessions, negating the need for a heart rate monitor.
Body composition and anthropometric measures were standing height, body mass, and body fat percentage, measured in the exercise physiology lab. Standing height was measured with a metric wall tape, set square, and wooden board (nearest 0.5 cm). Body mass and composition were measured on a Tanita BF 681W (bioelectrical impedance) body composition scale to the nearest 0.1 kg and 1% body fat. Body composition measurements were performed with the subject having clean bare feet, at the same time of day and with the same hydration level to ensure validity and reproducibility. Body composition was monitored to provide an indicator of training program effectiveness and because some research has suggested a relationship between CLBP and obesity (36).
The subjects were instructed concerning the exact performance of all laboratory tests before testing to ensure a safe technique and maximal effort. The researcher provided encouragement to all subjects in an attempt to elicit a maximal effort. The free-weight bench press was conducted on a flat bench with an Olympic-style bar and weights. The bench press test was a 10RM effort determined within 4 sets-that is, 1 warm-up set followed by 3 challenging sets of increasing load (kg). Its purpose was to determine upper-body strength. The rest time between each set was 3 minutes. The subject was positioned supine on the bench press. The subject grasped the bar with his or her hands approximately shoulder width apart, and then the subject extended his or her arms at the elbow, removing the bar up off the supports. The bar was then lowered (under control) to the chest, and then, in a smooth motion, it was pushed back up, extending the elbows and returning to the starting position. Lowering the bar to the chest and then pushing the bar back up to the start position was considered 1 repetition of that exercise; this was repeated 10 times (repetitions).
The Biering-Sorensen Back Endurance (BSBE) test was used to assess low-back isometric muscular endurance, which tends to be reduced in those with CLBP (29). The procedure for the BSBE test has been described previously (20). The subject was placed in a prone position on the horizontal plinth so that the iliac crest was at the breakpoint in the plinth. Two straps were fastened at the subject's gluteal and ankle regions. Once the subject was ready, the upper-body support was removed to initiate the BSBE. The subject's arms were folded across his or her chest for the duration of the test. A horizontally neutral position was maintained via contraction of the erector spinae, gluteal, and hamstring regions. The subject's position was monitored by the researcher. Once the subject was unable to maintain the necessary horizontal position for 2 seconds, the test was terminated. Each subject's RPE was assessed with the Borg scale (15-grade scale, anchors 6 and 20) at the completion of the BSBE.
The abdominal curl-up tests measured the muscular endurance of the abdominal muscles, which, as with low-back endurance, is suggested to be reduced in those with CLBP (29). The test was terminated when the subject was unable to maintain the required cadence or unable to maintain the proper curl-up technique for 2 consecutive repetitions despite feedback from the researcher. A maximum of 3 corrections were allowed by the appraiser before termination of the test. The subject was positioned supine with the head resting on the mat, arms straight at sides and parallel to the trunk, palms of hands in contact with the mat, and the middle finger tip of both hands at the 0 mark (identified by a piece of tape). Knees are bent at 90°, and the heels are kept in contact with the mat. The test is performed with shoes on. Cadence was set by a metronome (50 bpm). The test started with a slow curling up of the upper spine far enough so that the middle finger tips of both hands reached the 8-cm mark identified by tape. During the curl-up, the palms and heels remained in contact with the mat. On return, the shoulder blades and head had to contact the mat, and the finger tips of both hands had to touch the 0 mark. Each subject completed as many repetitions as possible.
Flexibility of the low back and hamstrings was assessed using the flexometer during a sit-and-reach test. The subjects warmed up for this test as it followed the o2max test. The subjects, without shoes, sat with their legs fully extended and the soles of their feet placed flat against the flexometer. Keeping their knees fully extended, arms evenly stretched, and palms down, the subjects bent and reached forward in a smooth, controlled effort and held for 2 seconds. The procedure was repeated twice, with the highest result recorded (nearest 0.5 cm).
Leg extension and flexion power were measured using the Cybex II isokinetic dynamometer (Cybex International, Medway, Mass). The Cybex was set for testing with the lever arm attached to the midline and the axis of rotation aligned with the anatomic axis of the knee's rotation. To stabilize the knee and hips, the subjects were seated in the Cybex chair with a back support and were strapped just superiorly to the knee and at the level of the pelvis. The angle of flexion at the hip joint was approximately 100°, with the starting position of the knee joint at 45° of flexion. Each subject crossed his or her chest with his or her arms and was asked to keep his or her upper body as still as possible while completing the repetitions. Knee extension and flexion power were measured unilaterally on the right leg. Once the equipment was calibrated for range of motion and weight of limb (i.e., lower leg), the subjects performed 3 warm-up repetitions. After the warm-up, the subjects performed 5 maximal voluntary contraction (extension-flexion) at 180°·s−1. The highest peak torque value was recorded in newton-meters (1).
The o2max test was conducted using an upright stationary Monarch cycle ergometer, with the purpose of monitoring the effectiveness and setting the intensity of the AT program. The protocol was incremental in nature, with 1-minute stages to o2max or volitional fatigue. Men started at a resistance of 1 kp, and women started at 0.5 kp, with increases of 0.5 kp per minute for both men and women. The subjects maintained pedal cadences between 60 and 65 rpm, with the exception of a sprint near the end of the test to elicit o2max. Each subject's RPE was recorded at the end of each 1-minute work stage (4). A ParvoMedics (Sandy, Utah) metabolic analyzer was used to measure breath-by-breath cardiorespiratory responses. The flowmeter was calibrated using a 3-L syringe of air. Heart rate (bpm) was recorded via a wireless Polar Heart Rate (Polar Electro Canada Inc, Lachine, Canada) chest monitor. The oxygen and carbon dioxide analyzers were calibrated pre- and posttest with commercial gases (16% oxygen, 4% carbon dioxide, balanced nitrogen). Criteria for o2max (2) were 1) an increase of < 100 ml·min−1 or decrease in o2 with increasing workload, 2) age-predicted (220 − age) maximal heart rate (HRmax), and 3) a respiratory exchange ratio ≥ 1.10. At termination of the o2max test, each subject cycled against minimal resistance for 5 minutes to assist with recovery.
Subjects completed health surveys at baseline, week 8, and week 16. These included the visual analog scale (VAS) for the degree of back pain felt by the subject during a typical week, the Oswestry Disability Index (ODI), and the Short-Form 36 Health Survey (SF-36). The VAS is a simple visual scale used to measure how much back pain each person felt (0 = no pain; 10 = maximal pain) (19). The ODI is a disease-specific outcome measure used in the management of spinal disorders (0 = no disability; 100 = maximum disability) (10). The SF-36 is a comprehensive measure of health status (QOL) that contains 36 items and that, when scored, yields 8 domains (parameters): physical functioning, physical role, bodily pain, general health, vitality, social functioning, emotional role, and mental health (6). The domains are scored on a scale from 0 (worst possible health) to 100 (best possible health). Physical functioning contains 10 items that assess physical activity limitations (e.g., climbing stairs). The role physical and role emotional domains measure work or daily activity problems that result from physical or emotional health problems. Bodily pain assesses limitations attributable to pain, whereas vitality measures energy and tiredness. The social functioning domain checks the effect of physical and emotional health on normal social activities. Mental health evaluates happiness, nervousness, and depression. The general health perceptions domain appraises personal health and the expectation of changes in health. These 8 parameters can be used to derive 2 composite scoring summaries: 1) physical composite summary (PCS: physical functioning, role physical, bodily pain, and general health perceptions) and 2) mental composite summary (MCS: vitality, social functioning, mental health, and role emotional) (37).
To assess test-retest reliability, intraclass correlations (ICCs) comparing baseline with week 16 were completed using the C group data. The following dependent variables were tested: sit-and-reach, bench press, BSBE, abdominal curl-up, leg extension, leg flexion, o2max, HRmax, ventilation max, PCS, and MCS (38). The results demonstrated a mean ICC of 0.87 and a range of 0.50-0.98. The control group data were used as opposed to the treatment groups (RT and AT) data because variation was expected within all groups but particularly within the treatment groups. Thus, analyses of the C group data were appropriate, but analyses of the treatment groups' data would compromise the validity of the ICC (Dr. Donald Sharpe, personal communication, 2008).
All values were reported as mean ± SD or percent change (%Δ). Age, height, body mass, body fat, bench press, sit-and-reach, BSBE, abdominal curl-up, RPE, peak leg extension and flexion power, o2max, HRmax, ventilation, respiratory exchange ratio, VAS, ODI, and SF-36 PCS and MCS were assessed via a general linear model with repeated-measures analysis of variance (ANOVA) to compare the RT and AT groups from baseline to week 8 and week 16. Similarly, a repeated-measures ANOVA was used to compare the RT, AT, and C groups from baseline to week 16 (the C group was not tested at week 8). Additionally, a Levene test for homogeneity of variances was completed on each dependent variable during the ANOVA, and, in each case, homogeneity of variance was found. Intraclass correlations between baseline and week 16 on the control group data were used as a measure of test-retest reliability. When a significant F ratio was achieved, post hoc comparisons were completed using a Fisher least significant difference. All differences were considered significant at an alpha of 0.05 (p ≤ 0.05).
No significant differences were apparent among the groups at baseline, week 8, or week 16 for body composition (i.e., body mass and body fat) (Table 1). Although there was no significant difference among the groups at any of the study's test points, there was a trend for the RT group to increase body mass while significantly decreasing body fat percentage from baseline to week 8 and from baseline to week 16 (Table 1). In contrast, the AT group significantly decreased both body fat percentage and body mass from baseline to week 16 (Table 1).
Muscular Strength, Endurance, Flexibility, and Power
At baseline, no significant differences were present among the 3 groups in strength, endurance, flexibility, or power. Similarly, no significant differences were noted between the RT and AT groups at week 8. However, by week 16, the RT group had significantly greater bench press strength and RPE score (on the BSBE) as compared with the C group (Table 4). When within-group comparisons (overtime) were conducted, it became evident that the RT group made many significant improvements, whereas the AT group's improvements were marginal. The RT group significantly increased bench press strength, BSBE time, and peak power on leg extension from baseline to week 8, from baseline to week 16, and from week 8 to week 16 (Table 4 and Figure 2). Additionally, sit-and-reach flexibility, RPE during the BSBE, abdominal curl-up endurance, and peak power on leg flexion were all significantly improved in the RT group from baseline to week 8 and from baseline and week 16. In contrast, the AT group showed significant improvements in sit-and-reach flexibility from baseline to week 8 and significant increases in peak leg extension and flexion power from baseline to week 8 and from baseline to week 16 (Table 4). The tendency throughout the course of the 16-week study was for the RT group to improve most muscular parameters from baseline to week 8, week 8 to week 16, and baseline to week 16, whereas this was not the case with the AT group.
At baseline, week 8, and week 16, no significant differences were found among the 3 groups on any of the cardiorespiratory variables (Table 5). The RT group did not make many significant improvements in the cardiorespiratory variables, demonstrating a singular but significant improvement in e (L·min−1) from baseline to week 8 and from baseline to week 16 (Table 5). However, as expected, the AT group showed significant increases in o2max (ml·kg−1·min−1) and e (L·min−1) from baseline to week 8 and from baseline to week 16, as well as a significant increase in e (L·min−1) from week 8 to week 16 (Table 5). Thus, the AT program improved the cardiorespiratory performance of the corresponding group, whereas the RT program did not.
Pain, Disability, and Quality of Life
By the study's conclusion (week 16), the RT groups showed significant improvements in the VAS, ODI, and SF-36 PCS and MCS scores compared with both the AT (Figure 3) and C groups, whereas the AT group displayed significant improvements in the ODI and SF-36 MPS compared with the C group (Table 6). Similarly, as the RT program significantly increased the muscular outcomes, it also benefited the levels of pain, disability, and overall QOL across time (within group). The RT group illustrated significant decrements in disability (i.e., ODI score) from baseline to week 8, from baseline to week 16, and from weeks 8 to 16 (Figure 3). Also, the RT group demonstrated significant reductions in pain (i.e., VAS score), and improved QOL (i.e., SF-36 PCS and MCS) from baseline to week 8 and from baseline to week 16 (Figure 3). In contrast, the AT group did not demonstrate any significant improvements in pain, disability, or QOL. It seems that improvements in pain, disability, and QOL may be associated with improvements in musculoskeletal fitness. However, because of subject numbers (n = 27), we were unable to perform a multiple regression analysis to directly address the potential relation between musculoskeletal variables and pain, disability, and QOL. Thus, we can only speculate that a temporal relationship exists.
This study sought to determine the effectiveness of 2 forms of periodized training-RT or AT-as rehabilitation strategies for those with CLBP. In general, the present data provided further support that periodized exercise training is effective at inducing meaningful changes in musculoskeletal strength, endurance, flexibility, and power, as well as aerobic fitness. However, the findings strongly signify that RT is a more efficacious mode of rehabilitation for CLBP, and thus the discussion will focus on the RT group. The development of musculoskeletal health via periodized RT improved body composition and reduced pain and disability, recovering QOL at the same time; this was not the case with the AT program.
Changes in body composition were marked by a 1.2% increase in body mass, with a 15% reduction in body fat percentage. Large improvements in muscular strength and endurance (27%), power (14%), and flexibility (10%) were noted with the RT group. Even more important were the reductions in pain (−63%) and disability (−67%) and improved QOL (12%) that were associated with RT. The findings suggest that traditional periodized RT typically used by athletes to reduce the risk of injury and improve athletic performance can also be applied broadly as a musculoskeletal rehabilitation tool for CLBP. It is likely that the early changes (∼8 weeks) in these musculoskeletal performance outcomes (i.e., strength, endurance, flexibility, and power) associated with the RT program were attributable largely to neural adaptations (12). After week 8, muscular hypertrophy became increasingly important, contributing to musculoskeletal performance in these middle-aged men and women subjects (13).
The influences of the periodized RT program on body composition and musculoskeletal outcomes have been demonstrated previously in a range of populations (22,23), but this may be the first study to demonstrate these improvements in a CLBP population. Similarly, the improved pain, disability, and QOL outcomes found in the RT group may be the first to be documented in the literature. Improvements in pain, disability, and QOL outcome measures have been found with other exercise rehabilitation programs (15,18,24) but not with periodized RT rehabilitation. Of note, these other exercise rehabilitation programs did not achieve the same amplitude of increase in muscular strength, endurance, flexibility, and power as did the present study.
Thus, the present findings are somewhat in contrast to those from previous CLBP exercise rehabilitation programs that used resistance, aerobic, flexibility training, and/or a combination of all and that had moderate success (18,24,27,31,35). So, why was this periodized RT rehabilitation program more effective than other programs to date? The basis for the mixed results in previous exercise rehabilitation studies and the results from the present study may reside in the 1) muscle groups exercised, 2) type of program, and 3) exercise selection.
First, this study did not focus on the core area; instead, it exercised the majority of the musculoskeletal system (Table 2). Focusing on the core area (i.e., rectus abdominus, internal and external obliques, and erector spinae muscles) is a common practice with many CLBP exercise rehabilitation programs (16,27). This may be a potential error in the rehabilitation of CLBP. It was an objective of this study to provide a whole-body workout that would sufficiently stress all large muscle groups to enhance the overall health of the musculoskeletal system and, consequently, improve physical function. The rationale for a whole-body exercise regime was to mimic programs used by athletes that train the entire body, such as during a preparatory phase of training. One of the goals of the preparatory phase is to develop work capacity and general physical preparation, with the development of general fitness being key (3). In the current study, the approach that was taken in the development of the RT program was to increase the overall strength and work capacity of the CLBP subjects but at a more gradual rate than those used among healthy athletes of the same age. The schema was to train the CLBP subjects as if they were chronologically and biologically middle aged, and experientially beginners, with the intent of developing a solid anatomic and physiological foundation.
Second, most previous CLBP exercise rehabilitation programs have used progressive overloads in which the resistance was gradually increased according to each subject's ability to complete more repetitions at given load than he or she could previously (17). On reaching the point at which more repetitions could be completed, the external load (resistance) was increased. This is a relatively typical practice in exercise rehabilitation. However, the present study used traditional periodization RT, which is a specific form of progressive overload training. The primary differences between periodized and nonperiodized progressive overload programs are the alternating loading schemes (8-10 and 12-15RM) over successive workouts, whereas a simple progressive overload program uses a traditional moderate-intensity loading scheme (10RM) with a constant relative intensity (23). Periodization is considered more effective at improving many attributes of athletic performance, such as muscular strength, endurance, and power as compared with nonperiodized training (23). Of note, in the current study, the RM was reduced compared with what would typically be implemented in a healthy young athlete, thus safeguarding against further injury or aggravation of the CLBP subjects' musculoskeletal system, as most were deconditioned before participating in the study.
Third, the present study employed a mixture of free-weight (dumbbells, barbells), machine, and body-weight exercises (Table 2). It is known that free-weight exercises are associated with greater fatigue in both the synergists and stabilizers because free-weight exercises are generally considered more neurally complex and taxing than machine-based exercises (7). The increased neural complexity associated with the free-weight component of the RT program likely resulted in the augmented muscular strength development (33).
In conclusion, many studies have examined the use of progressive overload exercise as a rehabilitative tool and have met with mixed results. To date, many of the training programs have focused on the core area and used body weight and/or machine devices to add the external resistance. However, the periodized RT program in the present study demonstrated substantial increases in muscular strength, endurance, flexibility, and power. The increases in most outcome measures were greater in the RT group than in the AT group. The improvements in musculoskeletal health translated into reduced pain, disability, and improved QOL. The data suggest 3 important points for rehabilitating CLBP: 1) use a periodized training program, 2) exercise a large proportion of the musculoskeletal system, and 3) use a combination of resistance methods (e.g., free weights). Future research should focus on periodized RT as a form of CLBP rehabilitation and should determine the upper and lower ranges of intensity and volume that facilitate improvements and maintenance of musculoskeletal health and the associated enhancements in pain, disability, and QOL in CLBP persons.
This study demonstrates that periodized RT can be applied to those with CLBP as a safe and effective form of rehabilitation. It is the same periodized training framework that is applied to a healthy or athletic population, with one exception: the program is more gradual in nature because of the disease state of the subjects. Consider a basic preparatory phase program that facilitates the anatomic and physiological readiness of the client and that progresses from this point according to regular musculoskeletal reassessments.
Support was provided by the Saskatchewan Health Research Foundation (New Investigator Grant) and the University of Alberta, Augustana Campus (travel grant). I am also indebted to Dr. Donald Sharpe for his assistance with the statistical analyses.
1. Adams, GM. Exercise Physiology Laboratory Manual
(4th ed.). Boston: McGraw Hill, 2002.
2. American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription
(7th ed.). Philadelphia: Lippincott Williams & Wilkins, 2006.
3. Bompa, TO. Periodization: Theory and Methodology of Training
(3rd ed.). Champaign: Human Kinetics, 1999.
4. Borg, G and Noble, B. Perceived exertion. Exerc Sport Sci Rev
2: 131-153, 1974.
5. Bouchard, C, Shephard, RJ, and Stephens, T. Physical Activity, Fitness, Health: Consensus State
. Champaign: Human Kinetics, 1994.
6. Brazier, JE, Harper, R, Jones, NM, O'Cathain, A, Thomas, KJ, Usherwood, T, and Westlake, L. Validating the SF-36 health survey questionnaire: new outcome measure for primary care. BMJ
305: 160-164, 1992.
7. Charette, SL, McEvoy, L, Pyka, G, Snow-Harter, C, Guido, D, Wiswell, RA, and Marcus, R. Muscle hypertrophy response to resistance training in older women. J Appl Physiol
8. Deyo, RA and Weinstein, JN. Low back pain. N Engl J Med
344: 363-370, 2001.
9. Donchin, M, Woolf, O, Kaplan, L, and Floman, Y. Secondary prevention of low-back pain. A clinical trial. Spine
15: 1317-1320, 1990.
10. Fairbank, JC, Couper, J, Davies, JB, and O'Brien, JP. The Oswestry low back pain disability
66: 271-273, 1980
11. Godin, G, Jobin, J, and Bouillon, J. Assessment of leisure time exercise behavior by self-report: a concurrent validity study. Can J Public Health
77: 359-362, 1986.
12. Hakkinen, A, Hakkinen, K, Hannonen, P, and Alen, M. Strength training
induced adaptations in neuromuscular function of premenopausal women with fibromyalgia: comparison with healthy women. Ann Rheum Dis
60: 21-26, 2001.
13. Hakkinen, K, Kallinen, M, Izquierdo, M, Jokelainen, K, Lassila, H, Malkia, E, Kraemer, WJ, Newton, RU, and Alen, M. Changes in agonist-antagonist EMG, muscle CSA, and force during strength training
in middle-aged and older people. J Appl Physiol
84: 1341-1349, 1998.
14. Hakkinen, K, Kraemer, WJ, Newton, RU, and Alen, M. Changes in electromyographic activity, muscle fibre and force production characteristics during heavy resistance/power strength training
in middle-aged and older men and women. Acta Physiol Scand
171: 51-62, 2001.
15. Hartigan, C, Rainville, J, Sobel, JB, and Hipona, M. Long-term exercise adherence after intensive rehabilitation for chronic low back pain. Med Sci Sports Exerc
32: 551-557, 2000.
16. Harts, CC, Helmhout, PH, De Bie, RA, and Staal, JB. A high-intensity lumbar extensor strengthening program is little better than a low-intensity program or a waiting list control group for chronic low back pain: a randomised clinical trial. Aust J Physiother
54: 23-31, 2008.
17. Houglum, PA. Muscle strength and endurance. In: Therapeutic Exercise for Musculoskeletal Injuries
. R.T. Pyrtel, ed. Champaign: Human Kinetics, 2005. pp. 197-259.
18. Iversen, MD, Fossel, AH, and Katz, JN. Enhancing function in older adults with chronic low back pain: a pilot study of endurance training. Arch Phys Med Rehabil
84: 1324-1331, 2003.
19. Jensen, MP, Miller, L, and Fisher, LD. Assessment of pain during medical procedures: a comparison of three scales. Clin J Pain
14: 343-349, 1998.
20. Kell, RT, Farag, M and Bhambhani, Y. Reliability of erector spinae oxygenation and blood volume responses using near-infrared spectroscopy in healthy males. Eur J Appl Physiol
91: 499-507, 2004.
21. Khalil, TM, Asfour, SS, Martinez, LM, Waly, SM, Rosomoff, RS, and Rosomoff, HL. Stretching in the rehabilitation of low-back pain patients. Spine
17: 311-317, 1992.
22. Kraemer, WJ, Hakkinen, K, Newton, RU, Nindl, BC, Volek, JS, McCormick, M, Gotshalk, LA, Gordon, SE, Fleck, SJ, Campbell, WW, Putukian, M, and Evans, WJ. Effects of heavy-resistance training on hormonal response patterns in younger vs. older men. J Appl Physiol
87: 982-992, 1999.
23. Kraemer, WJ, Hakkinen, K, Triplett-McBride, NT, Fry, AC, Koziris, LP, Ratamess, NA, Bauer, JE, Volek, JS, Mcconnell, T, Newton, RU, Gordon, SE, Cummings, D, Hauth, J, Pullo, F, Lynch, JM, Fleck, SJ, Mazzetti, SA, and Knuttgen, HG. Physiological changes with periodized resistance training in women tennis players. Med Sci Sports Exerc
35: 157-168, 2003.
24. Kuukkanen, T, Malkia, E, Kautiainen, H, and Pohjolainen, T. Effectiveness of a home exercise programme in low back pain: a randomized five-year follow-up study. Physiother Res Int
12: 213-224, 2007.
25. Lacey, R, Noels, A, Barden, J, Sharpe, D, Phenix, T, Martin, R, and Kell, RT. A comparison of traditional versus undulating strength training
programs. J Strength Cond Res
21: e29, 2007.
26. Mannion, AF. Fibre type characteristics and function of the human paraspinal muscles: normal values and changes in association with low back pain. J Electromyogr Kinesiol
9: 363-377, 1999.
27. Mannion, AF, Muntener, M, Taimela, S, and Dvorak, J. A randomized clinical trial of three active therapies for chronic low back pain. Spine
24: 2435-2448, 1999.
28. Noels, A, Lacey, R, Barden, J, Sharpe, D, Phenix, T, Martin, R, and Kell, RT. Improvements in strength following 12-weeks of periodized strength training
in males and females. J Strength Cond Res
21: e29, 2007.
29. Payne, N, Gledhill, N, Katzmarzyk, PT, and Jamnik, V. Health-related fitness, physical activity and history of back pain. Can J Appl Physiol
24: 236-249, 2000.
30. Pope, MH. Risk indicators in low back pain. Ann Med
21: 387-392, 1989.
31. Smeets, RJ, Vlaeyen, JW, Hidding, A, Kester, AD, Van Der Heijden, GJ, and Knottnerus, JA. Chronic low back pain: physical training, graded activity with problem solving training, or both? The one-year post-treatment results of a randomized controlled trial. Pain
134: 263-276, 2008.
32. Spenkelink, CD, Hutten, MM, Hermens, HJ, and Greitemann, BO. Assessment of activities of daily living with an ambulatory monitoring system: a comparative study in patients with chronic low back pain and nonsymptomatic controls. Clin Rehabil
16: 16-26, 2002.
33. Spennewyn, KC. Strength outcomes in fixed versus free-form resistance equipment. J Strength Cond Res
22: 75-81, 2008.
34. Spitzer, WO, Skovron, ML, Salmi, LR, Cassidy, JD, Duranceau, J, Suissa, S, and Zeiss, E. Scientific monograph of the Quebec Task Force on Whiplash-Associated Disorders: redefining “whiplash” and its management. Spine
20: 1S-73S, 1995.
35. Tritilanunt, T and Wajanavisit, W. The efficacy of an aerobic exercise and health education program for treatment of chronic low back pain. J Med Assoc Thai
84 (Suppl. 2): S528-S533, 2001.
36. Tsuritani, I, Honda, R, Noborisaka, Y, Ishida, M, Ishizaki, M, and Yamada, Y. Impact of obesity on musculoskeletal pain and difficulty of daily movements in Japanese middle-aged women. Maturitas
42: 23-30, 2002.
37. Ware, J and Sherbourne, C. The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection. Med Care
30: 473-483, 1992.
38. Weir, JP. Quantifying test-retest reliability using the intraclass correlation coefficient and the SEM. J Strength Cond Res
19: 231-240, 2005.
39. Zaryski, C and Smith, DJ. Training principles and issues for ultra-endurance athletes. Curr Sports Med Rep
4: 165-170, 2005.
Keywords:© 2009 National Strength and Conditioning Association
aerobic training; disability; strength training; therapy