Load-specific biomechanical adaptations to power-oriented resistance training in older adults
- Autores: Carlos Rodríguez López
- Directores de la Tesis: LUIS MARIA ALEGRE DURAN (dir. tes.), Robert Csapo (codir. tes.), Ignacio Ara Royo (tut. tes.)
- Lectura: En la Universidad de Castilla-La Mancha ( España ) en 2021
- Idioma: inglés
- Tribunal Calificador de la Tesis: Charlotte Suetta (presid.), Jesús García Pallarés (secret.), Francisco García García (voc.)
- Programa de doctorado: Programa de Doctorado en Investigación Sociosanitaria y de la Actividad Física por la Universidad de Castilla-La Mancha
- Materias:
- Enlaces
- Tesis en acceso abierto en: RUIdeRA
- Resumen
Background The global population aging phenomenon, caused by the low levels of fertility combined with the increase in life expectancy, is challenging the social and economic welfare for the next decades. Promoting older people to be and do what they reason to value (i.e., healthy aging) has been proposed as the best strategy to convert this challenge into an opportunity. For this purpose, it is necessary to prevent and delay disability derived from the progressive loss of intrinsic capacity, a composite of mental and physical function, with increasing age. The aging process results in structural and physiological changes in skeletal muscle that disrupt muscle function, and consequently, physical performance. The rate at which this biological process occurs can be accelerated by physical inactivity and chronic disease like knee osteoarthritis (KOA), or conversely, slowed by effective exercise strategies like power training (PT). In this sense, older people with KOA may have characteristical muscle function deficits that may require individualized PT by applying different intensities of load. Therefore, the main goals of the present PhD thesis were: 1) to assess limitations in muscle and physical performance of postmenopausal women with KOA (Study 1); 2) to compare the mechanical characteristics, neuromuscular demands between volume load-matched heavy- vs. light-load PT sessions in older adults, as well as the acute decline provoked in muscle function, physical performance, metabolic stress and muscle damage (Study 2 and 3), 3) to design a protocol for a series of studies comparing the long-term effects of heavy- vs. light-load PT in older adults. 4) to evaluate the effects after 12-weeks of volume load-matched heavy- vs. light-load PT on neuromuscular function and muscle morphology of older adults (Study 5) and 5) to explore the potential contralateral effects after 12 weeks of light vs. heavy load unilateral PT (Study 6).
Methods The present PhD thesis is composed by 6 studies in which voluntarily participated four different samples; postmenopausal women with KOA (n=18, 69.6±7.3 years) and their healthy age-matched controls (n=26, 66.1±7.7 years), and a couple of groups of older adults (A: n=15, 73.6±3.8 years and B: n=15, 70.6±4.2 years). Anthropometrics and body composition (assessed by dual x-ray absorptiometry) in combination with mid-thigh muscle size and muscle architecture (assessed by ultrasound) were evaluated. Muscle function of the lower limbs was examined through the force-velocity relationship and the force-time curve (through an isokinetic dynamometer, an isometric chair and a leg pres device, equipped with force and displacement sensors), occasionally combined with muscle excitation recording (by surface electromyography) while physical performance was assessed during functional tasks as rising up from a chair, stair climbing, maximal gait speed, and the timed-up and go test. Study 1 was a cross-sectional study comparing postmenopausal women with KOA and age-matched controls in terms of muscle and physical function. Study 2 and 3 used a cross-over design where subjects (group A) completed two volume load-matched PT sessions in a random order: a heavy- and light-load PT, separated by 7 days. Muscle function and excitation were registered pre, during, and post each PT session. For study 3, additional blood biomarkers of metabolic stress and muscle damage were collected pre, post, and 24h after PT. Study 4 presented the methods applied in Study 5 and Study 6, as part of the same project. Briefly, this was a within-person randomized control trial, including an 8-week control period followed by 12 weeks of PT. After complete the control period, the participants (group B) were randomized to three different study arms based on the treatment applied to their lower limbs during the PT period: (i) one leg completed a light-load PT (LL-PT) and the other leg no performed any exercise (LL-NE); (ii) one leg completed a heavy-load PT (HL-PT) and the other leg no performed any exercise (HL-NE); and (iii) one leg completed HL-PT and the other leg completed LL-PT. Changes in muscle function and morphology for each leg, as well as whole-body physical performance, were registered in the control and PT period. All the statistical analyses were performed according to standard procedures and the level of significance was set at α = 0.05.
Results Postmenopausal women with KOA showed reduced maximal isometric torque (Hedge’s g effect size (g)=1.05, p=0.001) and rate of torque development (g=0.77‒1.17, all p≤0.02), combined with impaired torque production at slow to moderate velocities (g=0.92‒1.70, p≤0.004), but not at high or maximal velocities (g=0.16, p>0.05). KOA were slower (g=0.81‒0.92, p≤0.011) and less powerful (g=1.11‒1.29, p≤0.001) during functional tasks. Additionally, knee-extensor deficits were moderately associated with power deficits in stair climbing (r=0.492‒0.659) (Study 1). From Study 2, more concentric mechanical work was performed in the LL training session, compared with HL (36.2±11.2%; p=0.001). Despite the higher mean EMG activity of the quadriceps femoris muscle (13.2±21.1%; p=0.038) and greater concentric force (35.2±7.6%; p=0.001) during HL, higher concentric velocity (41.0±12.7%, p=0.001) and a trend toward higher concentric power (7.2±18.9%, p=0.075) were found for LL. Relative velocity losses were similar in both sessions (~10%); however, relative force losses were only found in LL (7.4±6.5%, p=0.003). Additionally, performance declines were found after HL (Cohen’s d effect size (d); maximal isometric force=0.95 d; rate of force development=1.17 d; sit-to-stand power =0.38 d, all p<0.05) and LL (maximal isometric force=0.45 d; rate of force development=0.9 d; sit-to-stand power=1.17 d, all p<0.05), while lactate concentration increased only after LL (1.7 d, p=0.001). However, no differences were found between conditions (all p>0.05). Both conditions increased creatine kinase the day after exercise (marginal effect=0.75 d, p<0.001), but no other blood markers increased (all, p>0.05) (Study 3). Regarding long-term adaptations of PT (Study 5), HL-PT provoked greater improvements in maximal force capabilities (effect size (ES)=0.55‒0.68; p<0.001) than those observed after LL-PT (ES=0.27−0.47; p≤0.001) (post-hoc treatment effect, p≤0.057). By contrast, ES of changes in maximal shortening velocities were greater in LL-PT compared to HL-PT (ES=0.71, p<0.001 vs. ES=0.39, p<0.001), but this difference was not statistically significant. Both PT interventions elicited a moderate increase in maximum muscle power (ES=0.65‒0.69, p<0.001). Only LL-PT improved the early rate of force development (i.e., ≤100 ms) and muscle excitation (ES=0.36‒0.60, p<0.05). Increased muscle size was noted after both PT programs (ES=0.13‒0.35, p<0.035), whereas pennation angle increased only after HL-PT (ES=0.37, p=0.004). Unilateral PT provoked moderate improvements in maximal dynamic strength (d=0.35‒0.42; p<0.001), maximal muscle power (d=0.54‒0.66, p<0.001) and maximal shortening velocity (d=0.44‒0.68, p≤0.020) on the non-exercised contralateral limb of older adults, independently of the load used, while the isometric performance remained unchanged (p<0.05) (Study 6).
Conclusions Knee-extensor muscle weakness was presented in postmenopausal women with KOA, not only as limited maximal and rapid torque development during isometric contractions but also dynamically at low to moderate velocities. These deficits were related to impaired functional performance. The assessment of knee-extensor muscle weakness through the torque-time and torque-angular velocity relationships might enable individual targets for tailored exercise interventions in KOA (Study 1). For this purpose, HL PT seems to demand greater force and neural drive compared to LL PT, while both provoked a similar acute decline in neuromuscular and physical performance and is safe for older people (Study 2 and 3). In the long term, HL-PT seems to be more effective in improving the capability to generate large forces, whereas LL-PT appears to trigger greater gains in movement velocity in older adults. However, both interventions promoted similar increases in muscle power as well as muscle hypertrophy (Study 5). Moreover, both PT interventions induced significant muscle function adaptations in the contralateral non-exercised leg, turning it into a strategy to be considered to sparing of muscle strength after immobilization or in rehabilitation programs (Study 6).
