Impact of Mild Hypohydration on Muscle Endurance, Power, and Strength in Healthy, Active Older Men.

Goulet, EDB, Mélançon, MO, Lafrenière, D, Paquin, J, Maltais, M, and Morais, JA. Impact of mild hypohydration on muscle endurance, power, and strength in healthy, active older men. J Strength Cond Res 32(12): 3414-3424, 2018-Under particular circumstances older persons may be vulnerable to developing mild chronic hypohydration. In young adults, hypohydration has been shown to impair muscle endurance, power and strength. Muscle performance declines with aging, a condition known as dynapenia. How hypohydration impacts muscle performance in older persons remains unclear. In this study, we examined this question, believing it may identify a factor exacerbating dynapenia. One-hour after having been passively exposed to heat where either a body mass loss of 1% was induced or euhydration maintained with fluid ingestion, 8 healthy, active older men (age: 68 ± 5 years) completed an exercise testing session where indices of muscle strength (30-second chair stand, grip strength, maximal isometric seated leg-press extension), endurance (seated leg-curl flexion + seated leg-press extension to exhaustion at 60% of 1 repetition maximum), and power (30-second Wingate test) were assessed. Gastrointestinal temperature before exercise testing was not significantly different from that measured before heat exposure with neither hydration regimen. Magnitude-based inferential statistics indicate that from a clinical perspective, the effect of hypohydration on 30-second chair stand (-1.0 ± 4.4%) is possibly harmful, for grip strength (-2.4 ± 4.1%), lower limbs endurance (-7.5 ± 11.2%), and anaerobic power (-3.9 ± 4.3%) likely detrimental, and unclear with respect to maximal isometric lower limb strength. Maintaining adequate hydration in older men is important, since hypohydration of only 1% body mass could impede muscle endurance, power and strength and, consequently, worsen the impact of dynapenia.

Sleep depth and continuity before and after chronic exercise in older men: electrophysiological evidence.

During later life sleep depth (slow-wave sleep, SWS) and maintenance exhibit deleterious changes, with possible negative effects on daytime function. This study assessed the effect of chronic, supervised exercise on sleep using laboratory-based polysomnography (PSG) and repeated measures in older adults. Thirteen men aged 64±3served as their own controls and had their sleep measured for a total of 6 nights: 3 before and 3 after the 16-week training intervention. Each sequence involved 1 familiarization trial followed by 2 experimental nights (exercise night; nonexercise night) measured using 13-channel PSG (combined electroencephalography, electromyography, and electro-oculography). The exercise challenges consisted of inclined treadmill brisk walking (60min, 68-69% V˙O2peak). The intervention successfully improved some parameters of aerobic fitness, i.e. ventilatory thresholds 1 and 2 (P<0.05). Acute exercise triggered increases in circulating free fatty acids and lactate levels both at baseline and after the intervention (P<0.05). Noteworthy, acute exercise following training resulted in a 71% increase in SWS during subsequent sleep in comparison with the nonexercise condition before training, respectively 2.4% and 1.4% (P<0.05). Following training, acute exercise reduced total wake time by 30% and REM onset latency by 14% (P<0.05). Acute exercise improved sleep continuity by decreasing total wake time. These results show that aerobic training could increase sleep depth and continuity, during active days, in elderly men. In habitual exercisers, these effects of aerobic exercise on sleep, although modest, might counteract those resulting from aging.

Changes in markers of brain serotonin activity in response to chronic exercise in senior men.

Aging is associated with noticeable impairments in brain serotonin transmission, which might contribute to increased vulnerability to developing depression in later life. Animal and human studies have shown that aerobic exercise can stimulate brain serotonin activity and trigger parallel elevations in tryptophan (TRP, the serotonin precursor) availability in blood plasma. However, the influence of chronic exercise on serotonergic activity in older adults is not yet known. Sixteen men aged 64 ± 3 years exercised for 1 h (67%-70% peak oxygen consumption) at baseline and following 16 weeks of aerobic training. The main outcome measures were cardiorespiratory fitness, body composition, branched-chain amino acids (BCAA), TRP, prolactin, lactate, and free fatty acids (FFA). Changes in plasma free-TRP/BCAA and prolactin served as surrogates for TRP availability and serotonin activity, respectively. Chronic exercise decreased body mass (P < 0.05) whilst it increased ventilatory threshold 2 (P < 0.01). Although training did not affect plasma TRP availability to the brain at rest, both pre- and post-training exercise challenges markedly increased TRP availability (P < 0.001). The free-TRP/BCAA values reached a ceiling during exercise that was lower following training (P < 0.05), whereas similar patterns were found for prolactin, lactate, and FFA. These data show that aerobic exercise elicits consistent transient elevations in plasma TRP availability to the brain in older men; the elevations were independent from physical training, although less pronounced following training. The data support the contention that repeated elevations in brain serotonin activity might be involved in the antidepressant effect of exercise training in older adults.

Exercise increases tryptophan availability to the brain in older men age 57-70 years.

PURPOSE: Many aspects of serotonergic activity, both central and peripheral in origin, undergo significant changes with human aging. These alterations might predispose elderly people to develop mood disorders. Because previous work showed that increasing the peripheral availability of tryptophan (TRP) to the brain holds antidepressant properties, this study evaluated whether TRP availability to the brain is increased during prolonged exercise in older men. METHODS: Nineteen males age 64 ± 3 yr completed a treadmill exercise bout at an HR eliciting ∼68% V˙O(2peak) for 60 min. Fasting blood was collected at rest, after 30 and 60 min of exercise, and at 90 min (after exercise). Branched-chain amino acids (BCAA), total and free TRP, prolactin, ammonia, nonesterified fatty acids, glucose, and lactate were measured. RESULTS: Changes in free TRP/BCAA ratio and prolactin were used as peripheral proxies of central serotonin synthesis rate and activity. The free TRP/BCAA ratio observed at baseline was increased by 102% after 1 h of exercise (P < 0.0001) and remained elevated after exercise (78% above baseline, P < 0.001). The free TRP portion in serum increased from 2.8 ± 0.7 to 5.7 ± 1.8 µmol·L⁻¹ after 1 h of exercise (P < 0.001) and was strongly correlated with plasma nonesterified fatty acid contents (r17 = 0.887, P < 0.0001, all time points). Serum prolactin was significantly elevated after 1 h of exercise (8.6 ± 2.4 µg·L⁻¹, P < 0.001) and was positively correlated with free TRP/BCAA ratio (r16 = 0.48, P < 0.05, all time points). CONCLUSIONS: These results concur with previous observations in younger men and unveil that significant elevations in TRP availability to the brain are encountered during sustained exercise in older men. These results provide support to the hypothesis that increases in serotonin synthesis and activity might be involved in the antidepressant effect of exercise in the elderly.

Past-users of HRT are osteopenic four months after discontinuation:an observational and cross-sectional study.

Hormonal replacement therapy (HRT) helps to prevent osteoporosis. The effect of short-term discontinuation of a long-term HRT on bone mineral density (BMD) in healthy post-menopausal women is unknown. Fifteen women on HRT (HRT users), 17 who never used HRT (non-users) and 8 former HRT users (past-HRT users) were recruited. BMD was measured by DXA. Our results allow to hypothesize that BMD may decline after short-term HRT discontinuation, which would increase the fracture risks. Indeed, our results show that past-HRT users are osteopenic just as non-users. However, these results should be re-examined using a prospective trial and a larger sample size.

No sustained effect of aerobic or resistance training on insulin sensitivity in nonobese, healthy older women.

It is unclear whether long-term aerobic (AT) or resistance (RT) training can improve insulin sensitivity (IS) beyond the residual effect of the last training bout in older women (54-78 years). Therefore, a group of nonobese, healthy older women underwent 6 months of AT (n = 8) or RT (n = 10), and the authors measured IS 4 days after the last training bouts using the hyperinsulinemic-euglycemic clamp technique. Women trained 3 days/week. AT consisted of 25- to 60-min sessions of walking/jogging at 60-95% of maximal heart rate. RT consisted of three sets of nine exercises repeated 10 times at 80% of 1 repetition maximum. AT decreased fat mass, whereas both AT and RT increased fat-free mass. Neither training program, however, improved absolute or relative rates of glucose disposal. The authors therefore concluded that nonobese, healthy older women should perform AT or RT on a daily basis in order to improve IS and maintain the improvement.

Aerobic training improves insulin sensitivity 72-120 h after the last exercise session in younger but not in older women.

The regular practice of aerobic training (AT) induces an improvement in insulin sensitivity (IS) in healthy younger women that persists until 96-120 h after the last exercise bout. Due to the dearth of research data, it still remains unclear whether a regular AT program can improve IS for such a period of time after the last training bout in healthy older women. To address this issue, we trained 14 younger and 8 older women 3 days per week during 6 months, and measured IS 3-5 days after the last training bout. AT consisted of 25-60 min sessions of running at 60-95% of maximal heart rate. Fat mass decreased (8%) in older women only. VO(2max) and fat-free mass increased in both groups. Only older women decreased bodyweight (4%) and subcutaneous adipose tissue (19%). Visceral adipose tissue decreased in none of the groups. The IS improved only in younger women (relative: 22%; absolute: 24%). The present findings suggest that in older women the improvement in IS following AT is short-lived and results mainly from the acute effect of the last training bout, whereas in younger women the chronic adaptations induced by AT are implicated, as the improvement in IS is maintained beyond the residual effect of the last training bout. From a clinical standpoint, our findings suggest that in older women AT should be performed every day to improve glucose metabolism, whereas in younger women an AT frequency (three times per week) allowing to induce and maintain chronic minimal physiological adaptations would be required.

Age-related differences in metabolic adaptations following resistance training in women.

The purpose of this study was to determine whether aging alters changes in resting metabolic rate, body composition and insulin sensitivity in response to resistance training (RT) in women. The impact of a 6-month controlled RT program on fat-free mass (FFM), resting energy expenditure (REE), and glucose disposal was examined in 19 younger (27.8+/-3.5 yr; range 18-35) and 12 older (66.6+/-4.9 yr, range 55-70) non-obese caucasian women. For younger women, the RT program increased body weight (59.1+/-6.2 to 60.8+/-6.1 kg, p<0.05) due to an increase in FFM (39.2+/-3.7-40.4+/-3.2 kg, p<0.05). REE increased from 1379+/-114 to 1451+/-140 kcal day(-1), p<0.0001), and glucose disposal (from 364.1+/-91.1 to 402.1+/-87.8 mg min(-1), p<0.05). Neither fat mass nor VO2max changed significantly. On the other hand, older women lost fat mass (24.0+/-4.6-23.2+/-5.4 kg, p<0.05) and tended to gain FFM (from 37.3+/-4.0-38.0+/-4.3 kg, +1.9%; p=0.057), whereas no change occurred in body weight, REE, VO(2)max or glucose disposal. Thus, younger women showed greater metabolic changes in body composition, REE and insulin sensitivity in response to RT than older women. These results suggest an age-related alteration in metabolic changes in response to a 6-month RT program in previously untrained women.

Water-induced hyperhydration increases total body water to a greater extent than glycerol-induced hyperhydration: a case study of a trained triathlete.

Glycerol-induced hyperhydration (GIH) prior to endurance exercise is a strategy that is increasingly used by athletes. Compared with water-induced hyperhydration (WIH), GIH has been shown to reduce diuresis, thereby increasing total body water (TBW). It has never been demonstrated that WIH proved to be more efficient than GIH for increasing TBW. Therefore, we report the case of a trained triathlete in whom WIH, compared with GIH, increased TBW during a 110-min hydration protocol. On two separate days the subject ingested, in a randomized double blind fashion, either 26 ml.kg(-1) body mass (BM) of water or 26 ml.kg(-1) BM of water with 1.2 g glycerol.kg(-1) BM. Compared with GIH, WIH increased TBW by an additional 511 ml. It is proposed that WIH was effective in decreasing urine output and, therefore, in augmenting TBW, because the water ingested during this treatment was integrated into the body fluid pools relatively more slowly than that ingested during GIH. Practically, this finding implies that it could thus be possible for researchers and athletes to find out that on occasion WIH increases TBW more than GIH over a period of hydration of 2 h.