Muscle power increases after resistance training in growth-hormone-deficient adults

VCAM-1 upregulation accompanies muscle remodeling following resistance-type exercise in Snell dwarf (Pit1dw/dw ) mice

Snell dwarf mice (Pit1^dw/dw ) exhibit deficiencies in growth hormone, prolactin, and thyroid stimulating hormone. Besides being an experimental model of hypopituitarism, these mice are long-lived (>40% lifespan extension) and utilized as a model of slowed/delayed aging. Whether this longevity is accompanied by a compromised quality of life in terms of muscular performance has not yet been characterized. In this study, we investigated nontrained and trained muscles 1 month following a general validated resistance-type exercise protocol in 3-month-old Snell dwarf mice and control littermates. Nontrained Snell dwarf gastrocnemius muscles exhibited a 1.3-fold greater muscle mass to body weight ratio than control values although muscle quality, maximum isometric torque normalized to muscle mass, and fatigue recovery were compromised. For control mice, training increased isometric torque (17%) without altering muscle mass. For Snell dwarf mice, isometric torque was unaltered by training despite decreased muscle mass that rendered muscle mass to body weight ratio comparable to control values. Muscle quality and fatigue recovery improved twofold and threefold, respectively, for Snell dwarf mice. This accompanied a fourfold increase in levels of vascular cell adhesion molecule-1 (VCAM-1), a mediator of progenitor cell recruitment, and muscle remodeling in the form of increased number of central nuclei, additional muscle fibers per unit area, and altered fiber type distribution. These results reveal a trade-off between muscle quality and longevity in the context of anterior pituitary hormone deficiency and that resistance-type training can diminish this trade-off by improving muscle quality concomitant with VCAM-1 upregulation and muscle remodeling.

Threshold of chair stand power necessary to perform activities of daily living independently in community-dwelling older women

PURPOSE

To determine (1) the reproducibility of measurements of chair stand mean power (CSMP), (2) the relationships of CSMP with age, height, body mass, and body mass index, and (3) to identify the threshold of CSMP below which performing activities of daily living (ADL) is limited in older women.

METHODS

Eighty-seven older women (70-88 years) were divided into an independent group (n = 48) who needed no assistance and a dependent group (n = 39) who needed assistance to perform ADL. The CSMP expressed in watts (velocity × load) for each repetition was assessed by a device that measures mean velocity.

RESULTS

The intraclass correlation coefficient for CSMP suggested a high level of reproducibility (intra-class correlation coefficient = 0.88-0.92, P < .05). Relationships existed between CSMP and age (r = -0.37; P < .001), CSMP and height (r = 0.31; P < .001), CSMP and body mass (r = 0.43; P < .001), and CSMP and body mass index (r = 0.30; P < .001). A receiver operator characteristic curve analysis revealed the optimal threshold criteria; a CSMP of 214 watts resulted in the highest combination of sensitivity (82.1%) and specificity (81.2%).

CONCLUSION

The threshold of CSMP below which assistance is required to perform ADL in community-dwelling older women was identified.

Laterality of Hand Grip and Elbow Flexion Power in Right Hand–Dominant Individuals

Purpose:

This study aimed to compare the laterality, and its gender difference, of hand grip and elbow flexion power according to load in right hand–dominant individuals.

Results:

The subjects were 15 healthy young males (age 22.1 ± 0.7 y, height 171.3 ± 3.4 cm, mass 64.5 ± 4.1 kg) and 15 healthy young females (age 22.4 ± 1.0 y, height 161.1 ± 3.0 cm, mass 55.4 ± 4.6 kg). Isotonic peak power was measured with 6 different loads ranging from 20% to 70% of maximum voluntary contraction (MVC) for grip and elbow flexion movements.

Results:

The peak power was significantly larger in males than in females in both movements (ratio, males:females was 58.1:49.4%). The dominant right hand had larger peak power in all loads for hand grip power (ratio, dominant:nondominant was 83.6:71.1%) and in loads of 20% to 50% MVC for elbow flexion power (88.7:85.7%) in both genders, confirming laterality in both movements. The peak power ratio of the dominant right hand to the nondomi-nant left hand was significantly larger in hand grip than in elbow flexion for all loads in females.

Conclusion:

Even though laterality was confirmed in both grip and elbow flexion, gender difference is more marked in hand grip.

Short-term administration of supraphysiological recombinant human growth hormone (GH) does not increase maximum endurance exercise capacity in healthy, active young men and women with normal GH-insulin-like growth factor I axes

CONTEXT

Despite the fact that the use of GH as a doping agent in sports is widespread, little is known about its short-term effects.

OBJECTIVE

The objective was to study the effects of GH on exercise capacity.

DESIGN

A double-blind, placebo-controlled study was used, with a treatment period of 28 d.

SETTING

Subjects from general community studied ambulatory at a university hospital.

PARTICIPANTS

Thirty healthy active young normal volunteers (15 women and 15 men) were recruited by local announcement, and all completed the study.

INTERVENTION

All subjects were randomized to receive a low GH dose (0.033 mg/kg.d or 0.1 IU/kg.d), a high GH dose (0.067 mg/kg.d or 0.2 IU/kg.d), or placebo.

MAIN OUTCOME MEASURES

Power output and oxygen uptake on bicycle exercise were the main outcome measures.

RESULTS

We found no effect of the low or high dosages of GH on maximum oxygen uptake during exercise (mean +/- se for placebo, 45.2 +/- 1.6 to 45.2 +/- 2.1 ml/kg.min; GH low dose, 42.8 +/- 1.6 to 42.8 +/- 1.6 ml/kg.min; GH high dose, 44.8 +/- 3.4 to 44.8 +/- 2.2 ml/kg.min; not significant by two-way ANOVA). Neither was there any effect on maximum achieved power output during exercise or on blood pressure, heart rate, or the electrocardiographic ST level at rest or during exercise. GH significantly increased total body weight (P = 0.028), an effect predominantly ascribed to fluid retention (increased extracellular water volume), whereas muscle mass (as indicated by intracellular water volume) did not change. However, changes in the latter correlated to changes in physical performance, possibly due to different training efforts.

CONCLUSION

Administration of supraphysiological recombinant human GH during a period of 4 wk does not improve power output or oxygen uptake.

The effects of five-year growth hormone replacement therapy on muscle strength in elderly hypopituitary patients

OBJECTIVE

Little is known of the long-term effects of GH replacement therapy on muscle strength in elderly adults with adult onset GH deficiency (GHD). In this study, the effects of 5 years of GH replacement therapy on muscle function were determined in adults over 60 years of age with adult onset GHD.

DESIGN

A prospective, open-label, single-centre study. Patients Twenty-six (12 male and 14 female) consecutive hypopituitary adults with adult onset GHD, mean age 65.0 (range 61-74) years.

MEASUREMENTS

Upper leg muscle strength was measured using a Kin-Com dynamometer. Right and left handgrip strength were measured using an electronic grip force instrument.

RESULTS

The mean insulin-like growth factor-I (IGF-I) SD score increased from -1.10 at baseline to 1.21 at end of the study. Body weight was unchanged during the 5-year study. A sustained increase in lean body mass and a sustained reduction of body fat was observed as measured using dual-energy X-ray absorptiometry (DEXA). The GH replacement therapy induced a sustained increase in isometric (60 degrees ) knee flexor strength. After statistical correction for age and sex variables using observed/predicted value ratios, a sustained increase was also observed in concentric knee flexor strength at an angular velocity of 60 degrees /s, concentric knee extensor strength at 60 degrees /s and 180 degrees /s, and peak right handgrip strength. At baseline, knee flexor strength was 90-96% of predicted, knee extensor strength was 85-87% of predicted, and hand-grip strength was 74-80% of predicted values. At study end, knee flexor strength was 98-106% of predicted, knee extensor strength was 90-100% of predicted, and hand-grip strength was 80-87% of predicted values.

CONCLUSION

Elderly patients with adult onset GH deficiency had decreased baseline muscle strength also after correction for age and sex. The 5-year GH replacement therapy normalized knee flexor strength and improved, but did not fully normalize, knee extensor strength and handgrip strength.