Acute and Chronic Bone Marker and Endocrine Responses to Resistance Exercise With and Without Blood Flow Restriction in Young Men.

In this study, we compared acute and chronic bone marker and hormone responses to 6 weeks of low intensity (20% 1RM) blood flow restriction (BFR20) resistance training to high intensity (70% 1RM) traditional resistance training (TR70) and moderate intensity (45% 1RM) traditional resistance training (TR45) in young men (18-35 years). Participants were randomized to one of the training groups or to a control group (CON). The following training programs were performed 3 days per week for 6 weeks for knee extension and knee flexion exercises: BFR20, 20%1RM, 4 sets (30, 15, 15, 15 reps) wearing blood flow restriction cuffs around the proximal thighs; TR70, 70% 1RM 3 sets 10 reps; and TR45, 45% 1RM 3 sets 15 reps. Muscle strength and thigh cross-sectional area were assessed at baseline, between week 3 and 6 of training. Acute bone marker (Bone ALP, CTX-I) and hormone (testosterone, IGF-1, IGFBP-3, cortisol) responses were assessed at weeks 1 and 6, with blood collection done in the morning after an overnight fast. The main findings were that the acute bone formation marker (Bone ALP) showed significant changes for TR70 and BFR20 but there was no difference between weeks 1 and 6. TR70 had acute increases in testosterone, IGF-1, and IGFBP-3 (weeks 1 and 6). BFR20 had significant acute increases in testosterone (weeks 1 and 6) and in IGF-1 at week 6, while TR45 had significant acute increases in testosterone (week 1), IGF-1 (week 6), and IGFBP-3 (week 6). Strength and muscle size gains were similar for the training groups. In conclusion, low intensity BFR resistance training was effective for stimulating acute bone formation marker and hormone responses, although TR70 showed the more consistent hormone responses than the other training groups.

Physical activity, ambulation, and comorbidities in people with diabetes and lower-limb amputation.

We characterized physical activity (PA) and its relation to physical function and number of comorbidities in people with diabetes and transtibial amputation (AMP), people with diabetes without AMP, and nondisabled adults without diabetes or AMP. Twenty-two individuals with type 2 diabetes mellitus (DM) and transtibial amputation (DM+AMP), 11 people with DM, and 13 nondisabled participants were recruited for this cross-sectional cohort study. Measures included PA volume and intensity, a Timed Up and Go test, a 2-min walk test, and number of comorbidities. The nondisabled group performed greater amounts of PA than the DM group, who performed greater amounts of PA than the DM+AMP group. PA was related to physical function in the DM group and in the DM+AMP group, whereas no such relationship existed in the nondisabled group. PA was not related to number of comorbidities in any group. These findings suggest the ability to walk may affect overall performance of PA. Alternately, PA may alleviate walking problems. This possibility is of interest because issues with walking may be modifiable by improved levels and intensity of PA. PA's lack of relation to number of comorbidities suggests that factors beyond multiple morbidities account for group differences in PA.

Lower limb neuromuscular function and blood flow characteristics in AFO-using survivors of stroke.

BACKGROUND AND PURPOSE: Ankle-foot orthoses (AFOs) and gait aids are commonly used by survivors of stroke to ambulate, but they have not been used as inclusion or exclusion criteria for physiological studies. The purpose of this study was to examine differences in neuromuscular function and blood flow characteristics between the lower limbs of ambulatory, AFO-using survivors of stroke (n = 9). METHODS: The subjects were, on average, 14 years poststroke and had used an AFO for about 7 years. We used the following measures to assess both lower limbs: quadriceps muscular strength (manual muscle testing, 1RM), calf muscular endurance (single-leg heel raises), lower limb soft tissue composition and muscle cross-sectional area, calf resting blood flow (strain gauge plethysmography), and central neural drive of the plantar flexors (nerve stimulation). The sound limb was defined as the control. RESULTS: Quadriceps strength, triceps surae endurance, and calf cross-sectional area all were greater in the sound limb than in the affected limb (relative differences: 76.3% ± 16.6%, 146.4% ± 24.6%, and 25.6% ± 5.7%, respectively). In addition, resting blood flow, peak torque, and central neural drive of the plantar flexors were significantly greater (relative differences: 38.7% ± 5.9%, 94.4% ± 17.9%, and 43.6% ± 12.0%, respectively) in the sound calf. DISCUSSION: Our findings confirm that significant decrements in muscle performance, size, and blood flow persist in the affected limb many years after stroke despite a resumption of ambulation. CONCLUSIONS: This cohort of ambulatory AFO users exhibited large variations in functional abilities. We recommend that future studies in stroke survivors consider AFO use in their research designs.

Differences in tibia morphology between the sound and affected sides in ankle-foot orthosis-using survivors of stroke.

OBJECTIVE: To examine differences in tibia and proximal femur morphology between the affected and sound limbs in ankle-foot orthosis (AFO)-using survivors of stroke. DESIGN: Observational study. SETTING: A university bone density laboratory. PARTICIPANTS: Ambulatory, AFO-using survivors of stroke (N=9; age range, 55-74y; poststroke duration, 13.5±4.4y; AFO use, 6.5±1.4y). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Total body and hip areal bone mineral density (aBMD) and bone mineral content (BMC) were assessed by dual-energy x-ray absorptiometry. The 4%, 38%, and 66% sites of both tibias were measured with peripheral quantitative computed tomography for total, cortical, and trabecular volumetric BMD (vBMD) and BMC. Bone geometry, bone strength index (BSI), strength strain index (SSI), and minimum and maximum rotated moments of inertia (Imin, Imax) were determined. RESULTS: Total hip and trochanter BMC and aBMD were 7% to 19% greater on the sound side (P<.05). Total BMC and vBMD were 2% to 21% greater (P<.05) on the sound limb, depending on site. Trabecular BMC and vBMD and BSI values were 19%, 21%, and 31% higher (P<.05) on the sound limb at the 4% site. Cortical BMC and vBMD (P<.05), and cortical thickness (P<.01) were greater on the sound side at the 38% and 66% sites. Cortical area and bone strength (SSI, Imin) were greater (P<.05) at the 66% site. Endosteal circumferences were greater on the affected side (P<.01). CONCLUSIONS: Interlimb differences in bone characteristics after a stroke persist despite returning to ambulatory status with AFO use.

Effects of resistance training duration on muscular strength retention 6-month posttraining in older men and women.

BACKGROUND AND PURPOSE: Older individuals are at a greater risk for falling, and this risk has been linked to age-related declines in strength and balance. It has been demonstrated that older individuals can increase strength and function from properly designed, supervised training programs; however, little is known about the regressive effects of a detraining period in this participant population once the training intervention has ended. This study examined changes in strength 6 months after training following a 40- or 80-week supervised progressive resistance training program. METHODS: Of the 25 men and 44 women (aged 55-75 years) who returned for testing 6 months after training, 38 had continued to exercise on their own (Ex) and 31 stopped training (NoEx). This represents 40.8% of the original 169 participants that were contacted. Individual measures of strength were averaged to represent a measure of mean upper body or lower body strength. Changes in mean 1RM (one repetition maximum) strength and percent changes in strength were analyzed for PRE (pretraining), POST (posttraining), and 6MP (6 months post) time points by mixed-factor ANOVAs (analyses of variance). RESULTS: Upper and lower body strengths were still significantly higher than baseline values, 6MP training for both groups. However, the longer-duration (80 week) training program provided a greater, although non-statistically significant, ability to maintain strength at higher levels at 6MP training compared to the strength values obtained at the end of the two different training periods. In addition, lower body strength was better maintained than measures of upper body strength independent of initial training duration. DISCUSSION: : This study confirms that older individuals can tolerate a progressive strength training program of significant duration and that older individuals may undergo a regression of strength at a similar pace to young individuals. CONCLUSION: Supervised strength training represents an efficacious intervention for improving strength in older adults with residual benefits lasting longer than previously expected.

Hormone responses to a continuous bout of rock climbing in men.

Rock climbing is rapidly increasing in popularity as a recreational activity and as a competitive sport. Few studies have tested acute physiological responses to climbing, and no studies to date have tested hormone responses to a climbing-based workout. This study aimed to measure testosterone (T), growth hormone (GH), and cortisol (C) responses to continuous vertical climbing in young male rock climbers. Ten male rock climbers, aged between 21 and 30 years, climbed laps on a submaximal 55' climbing route for 30 min, or until exhaustion, whichever came first. Heart rate (HR) was recorded after every lap. Blood samples were collected by venipuncture before (Pre), immediately post (IP), and 15 min after the climbing exercise (P15) to assess blood lactate and plasma GH, T, and C. Subjects climbed 24.9 ± 1.9 min and 507.5 ± 82.5 feet. Peak HR was 182.1 ± 2.3 bpm, and lactate (Pre: 2.9 ± 0.6 mmol/dL, IP: 11.1 ± 1.0 mmol/dL) significantly (P < 0.05) increased from Pre to IP. T concentrations significantly (P < 0.05) increased from Pre (6.04 ± 0.31 ng/mL) to IP (7.39 ± 0.40 ng/mL) and returned to baseline at P15 (6.23 ± 0.33 ng/mL). Cortisol levels did not significantly change during the protocol. GH significantly (P < 0.01) increased from Pre (0.63 ± 0.17 ng/mL) to IP (19.89 ± 4.53 ng/mL) and remained elevated at P15 (15.03 ± 3.89 ng/mL). An acute, short-term bout of high-intensity continuous climbing was an effective exercise stimulus for elevating plasma testosterone and growth hormone levels in young males.