Unilateral lower limb suspension: integrative physiological knowledge from the past 20 years (1991–2011)

Hackney, Kyle J.; Ploutz‐Snyder, Lori L.

doi:10.1007/s00421-011-1971-7

Cited by 52 publications

(67 citation statements)

References 105 publications

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“…Regardless of the apparent mRNA differences in expression, no change in muscle CSA as measured by histological staining was seen with the vastus lateralis or soleus with 10 days of ULLS or ULLS+EX (data not shown). Previously, decreased muscle size as measured by MRI have reported varied outcomes ranging between 6 and 20% and may be due to the longer duration of unloading which was between 16 and 42 days of ULLS (22). The reader should be cautioned when making comparisons between morphometric analyses, as was done in the current study, and whole muscle CSA measured by MRI due to methodological differences (43).…”

Section: Discussionmentioning

confidence: 99%

Concurrent Exercise on a Gravity-Independent Device during Simulated Microgravity

Cotter

Haddad

et al. 2015

Medicine &Amp; Science in Sports &Amp; Exercise

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Purpose To examine the effect of a high-intensity concurrent training program utilizing a single gravity-independent device on maintaining skeletal muscle function and aerobic capacity during short-term unilateral lower limb suspension (ULLS). Methods Nineteen subjects (10 male; 9 female; 21.0 ± 2.5 yr, 65.4 ± 12.2 kg) were separated into 2 groups: 1) 10 day unilateral lower limb suspension only (ULLS; n = 9) and 2) 10 day ULLS plus aerobic and resistance training (ULLS+EX; n = 10). Exercise was performed on a single gravity-independent Multi-Mode Exercise Device (M-MED) with alternating days of high-intensity interval aerobic training and maximal exertion resistance training. Results Aerobic capacity increased by 7% in ULLS+EX (P < 0.05). Knee extensor and ankle plantar flexor three repetition max increased in the ULLS+EX group (P < 0.05) but this change was only different than ULLS in the plantar flexors (P < 0.05). Peak torque levels decreased with ULLS but were increased for the knee extensors and attenuated for the ankle plantar flexors with ULLS+EX (P < 0.05). A shift towards type IIx myosin heavy chain mRNA occurred with ULLS and was reversed with ULLS+EX in the vastus lateralis (P < 0.05) but not the soleus. Myostatin and atrogin increased with ULLS in both the vastus lateralis and soleus but this change was mitigated with ULLS+EX only in the vastus lateralis (P = 0.0551 for myostatin; P < 0.05 for atrogin). Citrate synthase was decreased in the soleus during ULLS but was increased with ULLS+EX (P < 0.05). Conclusion These results indicate that an M-MED class countermeasure device appears to be effective at mitigating the deconditioning effects of microgravity simulated during a modified-ULLS protocol.

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Section: Discussionmentioning

confidence: 99%

Concurrent Exercise on a Gravity-Independent Device during Simulated Microgravity

Cotter

Haddad

et al. 2015

Medicine &Amp; Science in Sports &Amp; Exercise

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“…Certainly, large reductions in activity and activation of a limb results in muscle atrophy and impaired muscle function for both men and women (Narici and de Boer, 2011, Hackney and Ploutz-Snyder, 2012). There is some, but limited, evidence that sex differences in muscle function and fatigability exist after a period of disuse (Ploutz-Snyder et al, in review).…”

Section: Mechanisms For Sex Differences In Muscle Fatiguementioning

confidence: 99%

Sex differences in human fatigability: mechanisms and insight to physiological responses

2014

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Sex-related differences in physiology and anatomy are responsible for profound differences in neuromuscular performance and fatigability between men and women. Women are usually less fatigable than men for similar intensity isometric fatiguing contractions. This sex difference in fatigability, however, is task specific because different neuromuscular sites will be stressed when the requirements of the task are altered, and the stress on these sites can differ for men and women. Task variables that can alter the sex difference in fatigue include the type, intensity and speed of contraction, the muscle group assessed, and the environmental conditions. Physiological mechanisms that are responsible for sex-based differences in fatigability may include activation of the motor neuron pool from cortical and subcortical regions, synaptic inputs to the motor neuron pool via activation of metabolically-sensitive small afferent fibres in the muscle, muscle perfusion, and skeletal muscle metabolism and fibre type properties. Non-physiological factors such as the sex bias of studying more males than females in human and animal experiments can also mask a true understanding of the magnitude and mechanisms of sex-based differences in physiology and fatigability. Despite recent developments, there is a tremendous lack of understanding of sex differences in neuromuscular function and fatigability, the prevailing mechanisms and the functional consequences. This review emphasises the need to understand sex-based differences in fatigability in order to shed light on the benefits and limitations that fatigability can exert for men and women during daily tasks, exercise performance, training and rehabilitation in both health and disease.

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“…However, given the cross-sectional nature of these data, it remains unknown whether a decline in the number of skeletal muscle satellite cells could be a cause or simply a consequence of muscle fibre atrophy. Alternative models that have been used regularly to study the underlying mechanisms of skeletal muscle disuse atrophy are short-term lower-or upperlimb immobilization [11][12][13][14][15][16][17]. These models allow the assessment of skeletal muscle atrophy in a longitudinal study design.…”

Section: Introductionmentioning

confidence: 99%

“…Lower-limb immobilization can be achieved by a number of methods, e.g. ULLS (unilateral lower limb suspension) [11,19,20], plastic knee brace [21,22] and full-leg cast [16,17,23,24]. In contrast with ULLS and brace immobilization, a plaster cast will result in the most severe local physical inactivity, and, as such, will yield the most robust physical-inactivity-induced reduction of muscle mass within a short time period.…”

Section: Introductionmentioning

confidence: 99%

Muscle disuse atrophy is not accompanied by changes in skeletal muscle satellite cell content

et al. 2013

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Muscle disuse leads to a considerable loss in skeletal muscle mass and strength. However, the cellular mechanisms underlying disuse-induced muscle fibre atrophy remain to be elucidated. Therefore we assessed the effect of muscle disuse on the CSA (cross-sectional area), muscle fibre size, satellite cell content and associated myocellular signalling pathways of the quadriceps muscle. A total of 12 healthy young (24±1 years of age) men were subjected to 2 weeks of one-legged knee immobilization via a full-leg cast. Before and immediately after the immobilization period and after 6 weeks of natural rehabilitation, muscle strength [1RM (one-repetition maximum)], muscle CSA [single slice CT (computed tomography) scan] and muscle fibre type characteristics (muscle biopsies) were assessed. Protein and/or mRNA expression of key genes [i.e. MYOD (myogenic differentiation), MYOG (myogenin) and MSTN (myostatin)] in the satellite cell regulatory pathways were determined using Western blotting and RT-PCR (real-time PCR) analyses respectively. The present study found that quadriceps CSA declined following immobilization by 8±2% (P<0.05). In agreement, both type I and type II muscle fibre size decreased 7±3% and 13±4% respectively (P<0.05). No changes were observed in satellite cell content following immobilization in either type I or type II muscle fibres. Muscle MYOG mRNA expression doubled (P<0.05), whereas MSTN protein expression decreased 30±9% (P<0.05) following immobilization. Muscle mass and strength returned to the baseline values within 6 weeks of recovery without any specific rehabilitative programme. In conclusion, 2 weeks of muscle disuse leads to considerable loss in skeletal muscle mass and strength. The loss in muscle mass was attributed to both type I and type II muscle fibre atrophy, and was not accompanied by a decline in satellite cell content.

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Unilateral lower limb suspension: integrative physiological knowledge from the past 20 years (1991–2011)

Cited by 52 publications

References 105 publications

Concurrent Exercise on a Gravity-Independent Device during Simulated Microgravity

Concurrent Exercise on a Gravity-Independent Device during Simulated Microgravity

Sex differences in human fatigability: mechanisms and insight to physiological responses

Muscle disuse atrophy is not accompanied by changes in skeletal muscle satellite cell content

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