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Maximal Strength Training in Postmenopausal Women With Osteoporosis or OsteopeniaMats P. Mosti,1 Nils Kaehler,2 Astrid K. Stunes,1 Jan Hoff,23 and Unni Syversen14Departments of ^Cancer Research and Molecular Medicine; and2Circulation and Medical Imaging, Norwegian University of Science and Technology, Trondheim, Norway; Departments of3Physical Medicine and Rehabilitation; and 4Endocrinology,St Olav s University Hospital HF, Trondheim, Norway

AbstractMosti, MP, Kaehler, N, Stunes, AK, Hoff, J, and Syversen, U. Maximal strength training in postmenopausal women with osteoporosis or osteopenia. J Strength Cond Res 27(10): 2879-2886, 2013-Current guidelines recommend weightbearing activities, preferably strength training for improving skeletal health in patients with osteoporosis. What type of strength training that is most beneficial for these patients is not established. Maximal strength training (MST) is known to improve 1-repetition maximum (1RM) and rate of force development (RFD), which are considered as important covariables for skeletal health. Squat exercise MST might serve as an effective intervention for patients with low bone mass. We hypothesized that 12 weeks of squat exercise MST would improve 1RM and RFD in postmenopausal women with osteoporosis or osteopenia and that these changes would coincide with improved bone mineral density (BMD) and bone mineral content (BMC), and serum markers of bone metabolism. The participants were randomized to a training group (TG, n = 10) or control group (CG, n = 11). The TG underwent 1 2 weeks of supervised squat exercise MST, 3 times a week, with emphasis on rapid initiation of the concentric part of the movement. The CG was encouraged to follow current exercise guidelines. Measurements included 1 RM, RFD, BMD, BMC, and serum bone metabolism markers; type 1 collagen amino-terminal propeptide (P1NP) and type 1 collagen C breakdown products (CTX). At posttest, 8 participants remained in each group for statistical analyses. The TG improved the 1RM and RFD by 154 and 52%, respectively. Lumbar spine and femoral neck BMC increased by 2.9 and 4.9%. The ratio of serum P1NP/CTX tended to increase (p = 0.09), indicating stimulation of bone formation. In conclusion, squat exercise MST improved 1RM, RFD, and skeletalAddress correspondence to Mats P. Mosti, mats.p.mosti@ntnu.no. 27(10)/2879-2886Journal of Strength and Conditioning Research 2013 National Strength and Conditioning Associationproperties in postmenopausal women with osteopenia or osteoporosis. The MST can be implemented as a simple and effective training method for patients with reduced bone mass.Key Words exercise, skeletal muscle, bone massIntroductionOsteoporosis is a chronic disease with the highest prevalence among postmenopausal women. These patients suffer increased fracture risk because of reduced bone mineral density (BMD) and impaired bone quality (23). Osteopenia refers to a condition where BMD values are between 1 and 2.5 SD below the average BMD of young women, whereas in osteoporosis, the BMD is 2.5 SD or more below the average. Sarcopenia refers to the skeletal muscle atrophy and weakness that often accompany aging. Osteoporosis and sarcopenia are both major contributors to the frailty syndrome, an age-related loss of physiological function that is most pronounced in women (9). Frailty leads to falls, and >90% of hip fractures among older adults are caused by falls from standing heights (9), causing disability and increased mortality (23).Current guidelines recommend strength training and weight-bearing exercises for preventing bone loss and maintaining bone mass in patients with osteoporosis (16). Strength training has been shown to maintain, or improve BMD in postmenopausal women, and strength training at high intensities seems to be most effective (10). Strength training has also been shown to promote increased levels of bone formation markers, for example, type 1 collagen amino- terminal propeptide (P1NP), and reduced levels of bone resorption markers, like, type 1 collagen C breakdown products (CTX) in the blood (19). However, what type of strength training is most efficient for improving skeletal health is not settled.A positive association between maximal muscle strength, measured as 1-repetition maximum (1RM) and bone mass has previously been reported (5,15). Strength training programs emphasizing improvements in the 1RM seem to beVOLUME 27 | NUMBER 10 | OCTOBER 2013 | 2879

effective for improving BMD and bone mineral content (BMC) in postmenopausal women (15,18). Power training, focusing on high-speed contractions, was in 1 study reported to be more effective than conventional strength training for reducing bone loss in postmenopausal women (24). Another study showed that neuromuscular performance robustly predicted bone strength in postmenopausal women (22). The latter finding suggests that rate of force development (RFD) capacity may also be important for skeletal adaptations from training. The RFD is considered as a fundamental part of muscular mechanical function and physical capacity (1). Lower extremity RFD is also associated with improved reaction speed and subsequent fall prevention (4). Altogether, these findings suggest that strength training interventions that improve both the 1RM and RFD are likely to be effective for promoting skeletal health in postmenopausal women.Maximal strength training (MST) is characterized by high loads and few repetitions, with special emphasis on fast mobilization of force in the concentric part of movement. The MST has previously been shown to improve lower extremity 1RM and RFD in elderly and diseased individuals (12,14,27). Because patients with reduced bone mass may benefit from both 1RM and RFD improvements, the MST may be an advantageous training method for these patients. Furthermore, the emphasis on high acceleration during muscle contraction may induce higher bone strains than conventional strength training, possibly ameliorating the osteogenic responses from training as previously suggested (24). The MST implemented in a squat exercise, with load resting on the shoulders, will induce an axial loading targeting the hip and spine, which are both sites prone to bone loss.To our knowledge, no studies have so far applied interventions combining heavy loads with high concentric acceleration as in MST, promoting both 1RM and RFD improvements. Most previous studies have also used training programs with a high volume of exercises, which may undermine compliance to the training program. Because the efficacy regarding squat exercise MST in patients with reduced bone mass is not yet known, this study aimed to examine this in patients with osteoporosis or osteopenia. We hypothesized that 12 weeks of squat exercise MST would improve 1RM and RFD in postmenopausal women with osteoporosis or osteopenia and that this would coincide with improvements in BMD, BMC, and serum levels of bone metabolism markers.MethodsExperimental Approach to the ProblemThis study was designed to investigate the effects of squat exercise MST on 1RM, RFD, and bone-related parameters in patients with osteoporosis or osteopenia. Peak oxygen consumption (VO2peak) was measured to control for possible changes in activity levels and concomitant alterations in aerobic fitness. Twenty-one patients with osteoporosis or2880Journal of Strength and Conditioning Research

Figure 1. Illustration of the squat machine and the positioning during testing and training.osteopenia volunteered to participate in the study. For each participant, measurements were obtained within 14 days before entry and 5 days after finishing the study. The participants were stratified by BMD T score and randomly allocated to a training group (TG, n =10) and a control group (CG, n = 11).The TG followed a training program consisting of supervised MST for 12 weeks, comprising 3 sessions each week for a total number of 36 sessions. In contrast to conventional strength training, MST focuses on high acceleration during the concentric phase, resulting in a high RFD during muscle contractions. The force-time profile of MSTTable 1. Participants characteristics.*Training group,Control group,

pretrainingpretraining

(n = 8)(n = 8)

Age (y)61.9 5.066.7 7.4

Height (cm)169.3 6.5162.9 6.3

Weight (kg)72.3 7.766.2 8.8

Body mass25.3 2.924.9 2.5

index

(kg-m-2)

T score

Lumbar spine-2.54 0.67-2.03 1.08

Femoral neck-1.81 0.78-2.03 0.44

Total hip-1.56 1.02-1.30 0.48

*Data are presented as mean SD.

Figure 2. Mean changes in (A) maximal squat strength (1-repetition maximum [1RM]) and rate of force development (RFD), (B) lumbar spine bone mineral content (BMC), (C) ratio between type 1 collagen amino- terminal propeptide (P1NP) and type 1 collagen C breakdown products (CTX). * = Different from pretraining within group, p < 0.05; # = difference between groups from pretraining to posttraining, p < 0.05; = difference between groups from pretraining to posttraining, p < 0.01.has been described previously (12). The training sessions consisted of 1 exercise, using the lower extremities in a squat exercise machine (Impulse Fitness IT 7006, Shandong, China). The exercise was executed from straight legs, down to a 90 angle in the knee joint and up again (Figure 1). The training session started with a warm-up including 2 sets of 8-12 repetitions at approximately 50% of the participants training load, followed by 4 sets of 3-5 repetitions at 85-90% of 1RM with special emphasis on maximal mobilization of force during the concentric part of movement. The participants were encouraged to perpetuate until fatigue. To assure sufficient progression of intensity, the participants training loads were evaluated each training session. If the participants could perform >5 repetitions, the training load was increased by 2.5 kg. Each set was separated by 2-3 minutes of rest. The CG was encouraged to follow current exercise guidelines for osteoporotic patients (16).SubjectsThe participants were recruited via their general practitioner, via advertisement in newspapers or from the outpatient clinic at the hospital. Women who were at least 2 years postmenopausal,