Key pointsr Disuse in older adults can critically decrease lower limb muscle power, leading to compromised mobility and overall quality of life.r We studied how muscle power and its determinants (muscle mass, single muscle fibre properties and motor control) adapted to 2 weeks of disuse and subsequent 2 weeks of physical training in young and older people.r Disuse decreased lower limb muscle power in both groups; however, different adaptations in single muscle fibre properties and co-contraction of leg muscles were observed between young and older individuals.r Six physical training sessions performed after disuse promoted the recovery of muscle mass and power. However, they were not sufficient to restore muscle power to pre-disuse values in older individuals, suggesting that further countermeasures are required to counteract the disuse-induced loss of muscle power in older adults.Enrico Rejc is presently Assistant Professor and Director of the Neuromuscular and Skeletal Research Core at the Kentucky Spinal Cord Injury Research Center, Department of Neurosurgery, University of Louisville, USA. Prior to taking this position, he was also involved in research activities at the University of Udine, University of California, Los Angeles, and Manchester Metropolitan University. He has studied the effects of disuse, ageing, spinal cord injury and physical exercise on the human neuromuscular system for about 10 years. His research is also focused on the recovery of motor function after severe spinal cord injury using spinal cord epidural stimulation and activity-based training. Stefano Lazzer is Professor and Director of the School of Sport and Exercise Sciences, Department of Medicine, University of Udine, Italy. He studies the physiology of muscle contraction, bioenergetics and cardio-respiratory adaptations to exercise on human health and performance. His current research programme is focused on the metabolic responses during exercise and the adaptation of humans disuse and training. Abstract Disuse-induced loss of muscle power can be detrimental in older individuals, seriously impairing functional capacity. In this study, we examined the changes in maximal explosive power (MEP) of lower limbs induced by a 14-day disuse (bed-rest, BR) and a subsequent 14-day retraining, to assess whether the impact of disuse was greater in older than in young men, and to analyse the causes of such adaptations. Sixteen older adults (Old: 55-65 years) and seven Young (18-30 years) individuals participated in this study. In a subgroup of eight Old subjects, countermeasures based on cognitive training and protein supplementation were applied. MEP was measured with an explosive ergometer, muscle mass was determined by magnetic resonance, motor control was studied by EMG, and single muscle fibres were analysed in vastus lateralis biopsy samples. MEP was ß33% lower in Old than in Young individuals, and remained significantly lower (−19%) when normalized by muscle volume. BR significantly affected MEP in Old (−15%) but not in Young. Retraini...

An acute use of foam rollers for SMFR performed immediately prior to running may negatively affect endurance running performance, but its use should be added before explosive motor performances that include stretch-shortening cycles.

Introduction The understanding of fatigue in hypoxia is limited due to: lack of control in arterial saturation, different exercise intensities and hypoxia levels, lag time between exercise cessation and fatigue evaluation. We aimed at evaluating fatigue during cycling and immediately after exhaustion (EXH) in normoxia, moderate and severe hypoxia at relative and absolute intensities. Methods Thirteen subjects completed three sessions in normoxia, moderate, and severe hypoxia with intensity based on percentage of normoxic maximal power output (NOR, MODABS, SEVABS) plus two sessions where intensity was based on the corresponding environmental condition (MODREL, SEVREL). Arterial saturation was clamped at 85% and 70% in moderate and severe hypoxia, respectively. Before, during cycling, and at EXH, maximum voluntary contraction (MVC), peripheral fatigue (high-frequency doublet [Db100], twitch [Pt]), and central fatigue (cortical voluntary activation [VATMS]) were evaluated without delay using an innovative ergometer. Results Time to EXH declined not only with hypoxia level at absolute but also relative intensities compared to NOR. At isotime, MVC, Pt, and Db100 were similarly depreciated in NOR, MODREL, and SEVREL. At EXH, there was a similar reduction among conditions in MVC (−26% to −31%), Db100 (−25% to −35%) and VATMS (−9% to −13%). However, Pt was less decreased in SEVREL compared with NOR (−33% ± 17% vs –46% ± 16%). Conclusions The shorter time to EXH in relative hypoxia and yet lower peripheral fatigue and similar central fatigue compared with normoxia suggests that hypoxia per se may affect brain areas not directly implicated in quadriceps motor function.

In this study, we investigated: i) the effects of bed rest and a subsequent physical training program on metabolic cost (Cw), mechanical work and efficiency during walking in older and young men; ii) the mechanisms underlying the higher Cw observed in older than young men.Twenty-three healthy male subjects (N = 16 older adults, age 59.6±3.4 years; N = 7 young, age: 23.1±2.9 years) participated in this study. The subjects underwent 14 days of bed rest followed by two weeks of physical training (6 sessions). Cw, mechanical work, efficiency, and co-contraction time of proximal muscles (vastus lateralis and biceps femoris) and distal muscles (gastrocnemius medialis and tibialis anterior) were measured during walking at 0.83, 1.11, 1.39, 1.67 m·s-1 before bed rest (pre-BR), after bed rest (post-BR) and after physical training (post-PT).No effects of bed rest and physical training were observed on the analysed parameters in either group. Older men showed higher Cw and lower efficiency at each speed (average +25.1 and -20.5%, P<0.001, respectively) compared to young. Co-contraction time of proximal and distal muscles were higher in older than in young men across the different walking speeds (average +30.0 and +110.3%, P<0.05, respectively).The lack of bed rest and physical training effects on the parameters analyzed in this study may be explained by the healthy status of both young and older men, which could have mitigated the effects of these interventions on walking motor function. On the other hand, the fact that older adults showed greater Cw, overall higher co-contraction time of antagonist lower limb muscles, and lower efficiency compared to the young cohort throughout a wide range of walking speed may suggest that older adults sacrificed economy of walking to improve stability.

This study confirms fatigue attenuation at isotime after training. Yet lower or similar fatigue at EXH indicates that, unlike previously suggested, fatigue tolerance may not be upregulated after 9 weeks of cycling training.