Effects of Different Percentages of Blood Flow Restriction on Muscle Oxygen Saturation While Walking.

The purpose of this investigation was to determine the effect of different relative pressures of blood flow restriction (BFR) on muscle oxygen saturation (SmO2) while walking at 3.0 mph (4.83 kph). Fifteen physically active healthy adults performed seven 5-minute stages of walking at 3.0 mph with a blood flow restriction cuff applied to the proximal portion of the left or right leg while bilateral SmO2 changes were measured using near infra-red spectroscopy (NIRS) on the medial head of the gastrocnemius (GM) and vastus lateralis (VL) muscles. Other measurements including heart rate (HR), blood pressure (BP), rating of perceived exertion (RPE), and ground contact time balance (GCTB) were also collected. SmO2 measurements were analyzed using two-way repeated measures (RM) ANOVA while other measurements were analyzed using one-way RM ANOVA. We observed a significant main effect of LOP% (limb occlusion pressure) on the difference in total area of desaturation that occurred during each occlusion stage (ADS), p < 0.0001 η2 = .336, early ΔSmO2, p < 0.0001 in both the GAS η2 = .132 and VL η2 = .335. The results suggest that there are significant differences in SmO2 desaturation between 40%, 80%, and 100% LOP. Our findings suggest that incremental increases in LOP will bring about greater SmO2 desaturation during walking and may therefore induce a larger adaptive response on the muscles. However, increased LOP% may intensify perception of effort.

Variation in cardiopulmonary restoration due to bodily posture post-submaximal exercise in collegiate athletes.

BACKGROUND: The body's anatomical position can influence the autonomic response to return to homeostasis following high intensity exercise. Discrepancies exist as to which body position is considered optimal and practical. This study intends to examine three recovery positions post submaximal exercise to determine which body position would be the most efficient in terms of excess post-exercise oxygen consumption and heart rate recovery. METHODS: NCAA Division I athletes (N.=17) from multiple sport teams completed three submaximal exercise tests utilizing the Bruce Protocol. Excess post-exercise oxygen consumption and heart rate recovery were measured at peak exercise and at 1-, 5-, and 10-minute time intervals during the recovery phase while assuming a recovery position: supine, trunk forward leaning, and standing vertical. RESULTS: Statistical analysis showed the 1-minute excess post-exercise oxygen consumption associated with supine recovery (1725±348 mL/kg) was significantly greater than standing vertical (1578±340 mL/kg, P=0.024). At 5 minutes, supine excess post-exercise oxygen consumption (3557±760 mL/kg) was significantly less than trunk forward leaning (4054±777 mL/kg, P=0.0001) and trunk forward leaning was significantly greater than standing vertical (3776±700 mL/kg, P=0.008). At 10 minutes, supine excess post-exercise oxygen consumption (5246±961 mL/kg) was significantly less than both the standing vertical position (5878±1042 mL/kg, P=0.0099), and the trunk forward leaning position (6749±1223 mL/kg, P<0.0001). Supine had the highest heart rate recovery at 1-, 5-, and 10-minutes post exercise. CONCLUSIONS: The supine position proved to be the most optimal during the 10-minute recovery period, while the trunk forward leaning position showed to be a more advantageous position for short-term recovery.

Muscle Oxygen Demands of the Vastus Lateralis in Back and Front Squats.

In resistance training squats are often used to strengthen the muscles of the lower extremities and core muscles. There are two common forms of squats that use a barbell for loading, the back squat and the front squat. The technique and loading of each squat differ markedly. However, the energetic demands on the muscle between the two forms are not well understood. The purpose of this study was to investigate the difference in energy demands between front and back squats by measuring the change in skeletal muscle oxygen saturation (SmO2) through the use of near infrared spectroscopy (NIRS). METHODS: Eleven resistance trained individuals, (5 female, 6 male) with an average age of 23.7 ± 1.4, completed 3 sets of 15 repetitions at 70% of their 1-RM weight for both back and front squats. Skeletal muscle oxygen saturation (SmO2) of the vastus lateralis was measured using a wireless NIRS device. RESULTS: The ΔSmO2 was not significantly different between back and front squats but was different between sets 1-3 (44.76 ± 3.24% vs. 55.19 ± 2.75% vs. 56.30 ± 2.63%), main effect p ≤ 0.0001. The recovery of SmO2 was significantly different between back (42.5 ± 3.4 sec) and front squats (30.9 ± 2.8 sec), main effect p ≤ 0.05. CONCLUSIONS: The findings of this study suggest that the energetic demands placed on the vastus lateralis during both front and back squats are similar with a slower recovery of energetics in the back squat.

Increased AMP deaminase activity decreases ATP content and slows protein degradation in cultured skeletal muscle.

BACKGROUND: Protein degradation is an energy-dependent process, requiring ATP at multiple steps. However, reports conflict as to the relationship between intracellular energetics and the rate of proteasome-mediated protein degradation. METHODS: To determine whether the concentration of the adenine nucleotide pool (ATP + ADP + AMP) affects protein degradation in muscle cells, we overexpressed an AMP degrading enzyme, AMP deaminase 3 (AMPD3), via adenovirus in C2C12 myotubes. RESULTS: Overexpression of AMPD3 resulted in a dose- and time-dependent reduction of total adenine nucleotides (ATP, ADP and AMP) without increasing the ADP/ATP or AMP/ATP ratios. In agreement, the reduction of total adenine nucleotide concentration did not result in increased Thr172 phosphorylation of AMP-activated protein kinase (AMPK), a common indicator of intracellular energetic state. Furthermore, LC3 protein accumulation and ULK1 (Ser 555) phosphorylation were not induced. However, overall protein degradation and ubiquitin-dependent proteolysis were slowed by overexpression of AMPD3, despite unchanged content of several proteasome subunit proteins and proteasome activity in vitro under standard conditions. CONCLUSIONS: Altogether, these findings indicate that a physiologically relevant decrease in ATP content, without a concomitant increase in ADP or AMP, is sufficient to decrease the rate of protein degradation and activity of the ubiquitin-proteasome system in muscle cells. This suggests that adenine nucleotide degrading enzymes, such as AMPD3, may be a viable target to control muscle protein degradation and perhaps muscle mass.

Short-term, high-fat diet accelerates disuse atrophy and protein degradation in a muscle-specific manner in mice.

BACKGROUND: A short-term high-fat diet impairs mitochondrial function and the ability of skeletal muscle to respond to growth stimuli, but it is unknown whether such a diet alters the ability to respond to atrophy signals. The purpose of this study was to determine whether rapid weigh gain induced by a high-fat (HF) diet accelerates denervation-induced muscle atrophy. METHODS: Adult, male mice (C57BL/6) were fed a control or HF (60 % calories as fat) diet for 3 weeks (3wHF). Sciatic nerve was sectioned unilaterally for the final 5 or 14 days of the diet. Soleus and extensor digitorum longus (EDL) muscles were removed and incubated in vitro to determine rates of protein degradation and subsequently homogenized for determination of protein levels of LC3, ubiquitination, myosin heavy chain (MHC) distribution, and mitochondrial subunits. RESULTS: When mice were fed the 3wHF diet, whole-body fat mass more than doubled, but basal (innervated) muscle weights, rates of protein degradation, LC3 content, mitochondrial protein content, and myosin isoform distribution were not significantly different than with the control diet in either soleus or EDL. However in the 14 day denervated soleus, the 3wHF diet significantly augmented loss of mass, proteolysis rate, amount of the autophagosome marker LC3 II, and the amount of overall ubiquitination as compared to the control fed mice. On the contrary, the 3wHF diet had no significant effect in the EDL on amount of mass loss, proteolysis rate, LC3 levels, or ubiquitination. Fourteen days denervation also induced a loss of mitochondrial proteins in the soleus but not the EDL, regardless of the diet. CONCLUSIONS: Taken together, a short-term, high-fat diet augments denervation muscle atrophy by induction of protein degradation in the mitochondria-rich soleus but not in the glycolytic EDL. These findings suggest that the denervation-induced loss of mitochondria and HF diet-induced impairment of mitochondrial function may combine to promote skeletal muscle atrophy.