Improving exercise tolerance in healthy young and older adults: possible role and mechanism of action of strength training

Increase exercise efficiency is essential to sustain independently, effectively and at adequate speed the daily movement tasks and to acquire the dose-dependant health benefits of an active lifestyle. Exercise tolerance can be regarded relevant for exercise prescription and sport performance both. In older people strength training intervention can be therefore considered the only mode of training, regardless oxidative metabolism effects, because is dose adapted and has low contraindication for untrained/ low fitness people. Purpose: test the hypothesis that a strength intervention will reduce the magnitude of the excessVO2 and the VO2SC in young and in older healthy adults . Methods: 16 young adults subjects and 21 older adults were recruited to participate in a randomized controlled trail, splitted in two groups and involved in a 4-weeks strength training. Force was measured during both a 1RM field test on squat and deadlift and, olnly for the young adults, during a maximal isometric laboratory test (IS) on a force platform . Oxygen consumption was measured in a ramp incremental test (modelled using a double-linear fit) and in tri-replicate during a CWR exercise performed at ∆50 (50% of the difference between the first ventilator threshold and the maximal oxygen consumption) (VO2 was modelled using a bi-exponential equation and the magnitude of the VO2SC quantified pre and post intervention). Young adults and older adults groups were compared using a two-way (time, group) analysis of variance. Results: the ability to produce force increased significantly in the strength-training group for both young and older adults 1RM (and IS test in the young adults), whereas no significant changes were observed in the control group (p > 0.05). In the young adults during the RI exercise, a significant excess VO2 (ml∙min-1) was present before training in the intervention group (∆CI around the mean difference [0.73, 5.15], d = 1.5, p = 0.02). This difference disappeared after strength training (∆CI [-2.96, 2.97], d = 0.01, p = 0.99). In the older adults no excess VO2 (ml∙min-1) was present before (∆CI [-0.87, 3.03], d = -0,08, p = 0.24). After training older adults presented an excess VO2 (ml∙min-1) (∆CI [-0.48, 4.28], d = -0,7, p = 0.02). In addiction ∆VO2/∆PO slope2 was significantly decreased (∆= 20%, p=0.004). Before training all young adults subjects exhibited a significant slow component (d = 3.05, p = 0.001, 95% CI [0.37, 0.88]). After training a significant reduction of the VO2SC (ml∙min-1) was observed in the intervention group (∆CI [-606, -351], d = -4.01, p = 0.001) with no difference detected for the control group (∆CI [-220, 145], d = -0.21, p = 0.68). The VO2SC reduction in the training group was associated with a 74±56% (8±5 min) increase in the time to reach exhaustion while no comparable gain was detected in the control group (3±17% or 0.5±2 min). In older adults VO2SC (ml∙min-1) was present before training ( in both training and control group) After training was observed a significant slow component for both training (∆CI [0.02, 0.93], d = 0.32, p = 0.001) and control group (∆CI [-2, -0.77], d = -0.4, p = 0.31). The older adults training group was associated with a increase 32±67% , 6±3 min in time to teach exsaustion. Conclusions: In agreement with our hypothesis, strength training in young adults induced lowering of the excess VO2 and VO2 slow component. On the contrary, in the elderly strength training may be responsible for a recovered ability to recruit type II muscle fibers that may increase their contribution towards force production in the heavy-intensity domain of an incremental cycling exercise.That ability may increase also their contribution towards force production in the heavy-intensity domain during a constant work rate cycling exercise. This findings are relevant in terms of performance during everyday life, sporting activities and exercise prescription.