Human single muscle fibre function with 84 day bed‐rest and resistance exercise

Abstract

Muscle biopsies were obtained from the vastus lateralis before and after 84 days of bed-rest from six control (BR) and six resistance-exercised (BRE) men to examine slow-and fast-twitch muscle fibre contractile function. BR did not exercise during bed-rest and had a 17 and 40% decrease in whole muscle size and function, respectively. The BRE group performed four sets of seven maximal concentric and eccentric supine squats 2-3 days per week (every third day) that maintained whole muscle strength and size. Slow (MHC I) and fast (MHC IIa) muscle fibres were studied at 15• C for diameter, peak force (P o ), contractile velocity (V o ) and force-power parameters. SDS-PAGE was performed on each single fibre after the functional experiments to determine MHC isoform composition. MHC I and IIa BR fibres were, respectively, 15 and 8% smaller, 46 and 25% weaker (P o ), 21 and 6% slower (V o ), and 54 and 24% less powerful after bed-rest (P < 0.05). BR MHC I and IIa P o and power normalized to cell size were lower (P < 0.05). BRE MHC I fibres showed no change in size or V o after bed-rest; however, P o was 19% lower (P < 0.05), resulting in 20 and 30% declines (P < 0.05) in normalized P o and power, respectively. BRE MHC IIa fibres showed no change in size, P o and power after bed-rest, while V o was elevated 13% (P < 0.05). BRE MHC IIa normalized P o and power were 10 and 15% lower (P < 0.05), respectively. MHC isoform composition shifted away from MHC I fibres, resulting in an increase (P < 0.05) in MHC I/IIa (BR and BRE) and MHC IIa/IIx (BR only) fibres. These data show that the contractile function of the MHC I fibres was more affected by bed-rest and less influenced by the resistance exercise protocol than the MHC IIa fibres. Considering the large differences in power of human MHC I and IIa muscle fibres (5-to 6-fold), the maintenance of whole muscle function with the resistance exercise programme is probably explained by (1) the maintenance of MHC IIa power and (2) the shift from slow to fast (MHC I → MHC I/IIa) in single fibre MHC isoform composition.

A critical benefit analysis of artificial gravity as a microgravity countermeasure

“…(Unpublished) actually increased MVC compared to pre-bed rest. The control groups of the shorter duration studies of Akima et al 2005, Suzuki et al 1994, andWu et al (Unpublished) (20, 20, and 30 days, respectively) did not significantly change post-versus pre-bed rest whereas the control group of the 90-day duration study of Trappe et al 2004 did decondition significantly.…”

“…As in Figure 40, the AG study ) represents the average fiber CSA for all fiber types while the resistive exercise studies represent only the change in diameter of type IIa fibers. All resistive countermeasures - Trappe et al 2007 (alternating squats and LBNP w/ treadmill), Bamman et al 1998 (squats), and Trappe et al 2004 (squats) -successfully maintained type IIa fiber diameter. Figure 42B shows the change in type IIa/IIx fiber CSA of the VL in rhesus monkeys.…”

“…Alternating days of LBNP with a vertical treadmill and squats / calf presses (Trappe et al 2004) was not an effective countermeasure for soleus Po;…”

Human soleus single muscle fiber function with exercise or nutrition countermeasures during 60 days of bed rest

“…This study was the first to show a complete exercise countermeasure for whole muscle (55) and myocellular properties (54) with prolonged unloading. These findings built on our findings from a previous 90-day bed rest study using only resistance exercise (52), demonstrating that aerobic and resistance exercise was complimentary for protecting the slow-twitch muscle fibers without interfering with the preservation of fast-twitch fibers. This was an important finding given that the combination of aerobic and resistance exercise attenuates muscle mass and strength gains in normal ambula-tory subjects (18,27).…”

“…Numerous animal studies (17,24,30,58) have not been able to completely protect soleus muscle mass and function during unloading using a wide range of resistive-type muscle loading paradigms. In humans, slow-twitch muscle fiber size and contractile function are only partially protected (ϳ50%) with resistance exercise during long-term bed rest (52). Thus, leg muscles containing slow-twitch fibers, particularly the soleus, need to be targeted by an exercise prescription program beyond previous resistance exercise-related programs.…”