Effects of high-intensity training and acute exercise on in vitro function of rat sarcoplasmic reticulum

Effects of exhaustive whole-body exercise and caffeine ingestion on muscle contractile properties in healthy men

BACKGROUND

The influence of exhaustive whole-body exercise and caffeine ingestion on electromechanical delay (EMD) has been underexplored. This study investigated the effect of exhaustive cycling exercise on EMD and other parameters of muscle contractile properties and the potential ability of caffeine to attenuate the exercise-induced impairments in EMD and muscle contractile properties.

METHODS

Ten healthy men cycled until exhaustion (88±2% of V̇O2max) on two separate days after ingesting caffeine (5 mg.kg-1 of body mass) or cellulose (placebo). Parameters of muscle contractile properties of the quadriceps muscles were assessed via volitional and electrically evoked isometric contractions, performed before and 50 minutes after ingestion of the capsules, and after exercise. Muscle recruitment during volitional contractions was determined via surface electromyography.

RESULTS

Exhaustive cycling exercise did not affect volitional and relaxation EMD (P>0.05) but increased evoked EMD. In addition, the exhaustive cycling exercise also increased muscle recruitment at the beginning of volitional isometric muscle contraction (P<0.05). The peak twitch force, maximal rate of twitch force development, and twitch contraction time were all compromised after exhaustive cycling exercise (P<0.05). Acute caffeine ingestion had no effect on muscle contractile properties (P>0.05), except that caffeine increased twitch contraction time at postexercise (P<0.05).

CONCLUSIONS

Exercise-induced decline in peripheral components of the EMD might be compensated by an increase in the muscle recruitment. In addition, acute caffeine ingestion had minimal influence on exercise-induced changes in muscle contractile proprieties.

Left atrial mechanics and aortic stiffness following high intensity interval training: a randomised controlled study

PURPOSE

High intensity interval training (HIIT) has been shown to improve important health parameters, including aerobic capacity, blood pressure, cardiac autonomic modulation and left ventricular (LV) mechanics. However, adaptations in left atrial (LA) mechanics and aortic stiffness remain unclear.

METHODS

Forty-one physically inactive males and females were recruited. Participants were randomised to either a 4-week HIIT intervention (n = 21) or 4-week control period (n = 20). The HIIT protocol consisted of 3 × 30-s maximal cycle ergometer sprints with a resistance of 7.5% body weight, interspersed with 2-min of active unloaded recovery, three times per week. Speckle tracking imaging of the LA and M-Mode tracing of the aorta was performed pre and post HIIT and control period.

RESULTS

Following HIIT, there was significant improvement in LA mechanics, including LA reservoir (13.9 ± 13.4%, p = 0.033), LA conduit (8.9 ± 11.2%, p = 0.023) and LA contractile (5 ± 4.5%, p = 0.044) mechanics compared to the control condition. In addition, aortic distensibility (2.1 ± 2.7 cm² dyn^-1 10³, p = 0.031) and aortic stiffness index (- 2.6 ± 4.6, p = 0.041) were improved compared to the control condition. In stepwise linear regression analysis, aortic distensibility change was significantly associated with LA stiffness change R² of 0.613 (p = 0.002).

CONCLUSION

A short-term programme of HIIT was associated with a significant improvement in LA mechanics and aortic stiffness. These adaptations may have important health implications and contribute to the improved LV diastolic and systolic mechanics, aerobic capacity and blood pressure previously documented following HIIT.

Effect of different intensities of physical activity on cardiometabolic markers and vascular and cardiac function in adult rats fed with a high-fat high-carbohydrate diet

BACKGROUND

Physical activity (PA) and diet are 2 lifestyle factors that affect cardiometabolic risk. However, data on how a high-fat high-carbohydrate (HFHC) diet influences the effect of different intensities of PA on cardiometabolic health and cardiovascular function in a controlled setting are yet to be fully established. This study investigated the effect of sedentary behavior, light-intensity training (LIT), and high-intensity interval training (HIIT) on cardiometabolic markers and vascular and cardiac function in HFHC-fed adult rats.

METHODS

Twelve-week-old Wistar rats were randomly allocated to 4 groups (12 rats/group): control (CTL), sedentary (SED), LIT, and HIIT. Biometric indices, glucose and lipid control, inflammatory and oxidative stress markers, vascular reactivity, and cardiac electrophysiology of the experimental groups were examined after 12 weeks of HFHC-diet feeding and PA interventions.

RESULTS

The SED group had slower cardiac conduction (p = 0.0426) and greater thoracic aortic contractile responses (p < 0.05) compared with the CTL group. The LIT group showed improved cardiac conduction compared with the SED group (p = 0.0003), and the HIIT group showed decreased mesenteric artery contractile responses compared with all other groups and improved endothelium-dependent mesenteric artery relaxation compared with the LIT group (both p < 0.05). The LIT and HIIT groups had lower visceral (p = 0.0057 for LIT, p = 0.0120 for HIIT) and epididymal fat (p < 0.0001 for LIT, p = 0.0002 for HIIT) compared with the CTL group.

CONCLUSION

LIT induced positive adaptations on fat accumulation and cardiac conduction, and HIIT induced a positive effect on fat accumulation, mesenteric artery contraction, and endothelium-dependent relaxation. No other differences were observed between groups. These findings suggest that few positive health effects can be achieved through LIT and HIIT when consuming a chronic and sustained HFHC diet.

Light-intensity and high-intensity interval training improve cardiometabolic health in rats

Physical activity has the potential to reduce cardiometabolic risk factors but evaluation of different intensities of physical activity and the mechanisms behind their health effects still need to be fully established. This study examined the effects of sedentary behaviour, light-intensity training, and high-intensity interval training on biometric indices, glucose and lipid metabolism, inflammatory and oxidative stress markers, and vascular and cardiac function in adult rats. Rats (12 weeks old) were randomly assigned to 1 of 4 groups: control (CTL; no exercise), sedentary (SED; no exercise and housed in small cages to reduce activity), light-intensity trained (LIT; four 30-min exercise bouts/day at 8 m/min separated by 2-h rest period, 5 days/week), and high-intensity interval trained (HIIT, four 2.5-min work bouts/day at 50 m/min separated by 3-min rest periods, 5 days/week). After 12 weeks of intervention, SED had greater visceral fat accumulation (p < 0.01) and slower cardiac conduction (p = 0.04) compared with the CTL group. LIT and HIIT demonstrated beneficial changes in body weight, visceral and epididymal fat weight, glucose regulation, low-density lipoprotein cholesterol, total cholesterol, and mesenteric vessel contractile response compared with the CTL group (p < 0.05). LIT had significant improvements in insulin sensitivity and cardiac conduction compared with the CTL and SED groups whilst HIIT had significant improvements in systolic blood pressure and endothelium-independent vasodilation to aorta and mesenteric artery compared with the CTL group (p < 0.05). LIT and HIIT induce health benefits by improving traditional cardiometabolic risk factors. LIT improves cardiac health while HIIT promotes improvements in vascular health.

Development of a neuromuscular electrical stimulation protocol for sprint training

PURPOSE

Sprint training is associated with several beneficial adaptations in skeletal muscle, including an enhancement of sarcoplasmic reticulum (SR) Ca(2+) release. Unfortunately, several patient populations (e.g., the elderly, those with cardiac dysfunction) that might derive great benefit from sprint exercise are unlikely to tolerate it. The purpose of this report was to describe the development of a tolerable neuromuscular electrical stimulation (NMES) protocol that induces skeletal muscle adaptations similar to those observed with sprint training.

METHODS

Our NMES protocol was modeled after a published sprint exercise protocol and used a novel electrode configuration and stimulation sequence to provide adequate training stimulus while maintaining subject tolerance. Nine young, healthy subjects (four men) began and completed the training protocol of the knee extensor muscles.

RESULTS

All subjects completed the protocol, with ratings of discomfort far less than those reported in studies of traditional NMES. Training induced significant increases in SR Ca(2+) release and citrate synthase activity (~16% and 32%, respectively), but SR Ca(2+) uptake did not change. The percentage of myosin heavy chain IIx isoform was decreased significantly after training. At the whole muscle level, neither central activation nor maximum voluntary isometric contraction force were significantly altered, although isometric force did exhibit a trend toward an increase (~3%, P = 0.055). Surprisingly, the NMES training produced a significant increase in muscle cross-sectional area (~3%, P = 0.04).

CONCLUSIONS

It seems that an appropriately designed NMES protocol can mimic many of the benefits of sprint exercise training, with a low overall time commitment and training volume. These findings suggest that NMES has the potential to bring the benefits of sprint exercise to individuals who are unable to tolerate traditional sprint training.

Specific effects of endurance and sprint training on protein expression of calsequestrin and SERCA in mouse skeletal muscle

Calsequestrin (CSQ) is the main Ca²⁺ binding protein inside the sarcoplasmic reticulum (SR) of skeletal and cardiac muscle. The present study demonstrates the specific effects of different training regimens on CSQ isoform 1 (CSQ1, the primary isoform) and SR Ca²⁺-ATPase (SERCA1, 2) expression in various skeletal muscles of mouse. CSQ1, SERCA1, and SERCA2 protein expression was determined with Western blot in m. soleus (SOL), m. extensor digitorum longus (EDL), m. gastrocnemius (GAS), m. rectus femoris (RF), and m. tibialis anterior (TA) muscles after completing a 6-week endurance or sprint training program. Endurance training induced decrease in CSQ1 concentration in SOL (p < 0.001) and in SERCA1 levels in GAS (p < 0.05), whereas increase in CSQ1 expression was detected in EDL (p < 0.01). After sprint training the concentration of CSQ1 increased in GAS (p < 0.01) and EDL (p < 0.01). Additionally, sprint exercise induced an increase in SERCA1 in GAS (p < 0.001) and a decline in TA (p < 0.05). SERCA2 was up-regulated with sprint training in GAS (p < 0.01). Myosin heavy chain (MHC) based fibre type composition altered differently depending on the muscle and the training regimen.These results indicate that (1) diverse training strategies used affect differently CSQ1 and SERCA1 concentrations in the skeletal muscle, (2) the regulation of CSQ1 and SERCA1 does not necessary follow the fast-slow definition despite the correlation between MHC isoforms, and (3) the changes in CSQ1 concentration occur prior to SERCA1 or SERCA2.

Alterations in peripheral muscle contractile characteristics following high and low intensity bouts of exercise

The aim of this study was to monitor muscle contractile performance in vivo, using an electrical stimulation protocol, immediately following an acute high and low intensity exercise session conducted at the same average intensity performed on a cycle ergometer. Eighteen healthy males (25.1 ± 4.5 years, 81.6 ± 9.8 kg, 1.83 ± 0.06 m; mean ± SD) participated in the study. On two occasions, separated by 1 week, subjects completed a high and low intensity exercise session in a random order on a cycle ergometer, performing equal total work in each. At the end of each test, a muscle performance test using electrical stimulation was performed within 120 s. Post-exercise muscle data were compared to the subjects' rested muscle. We found a reduction in muscle contractile performance following both high and low intensity exercise protocols but a greater reduction in maximal voluntary contraction (MVC) (P < 0.01), rate of torque development (RTD) (P < 0.001), rate of relaxation (RR(½)), (P < 0.001) the 60 s slope of the fatigue protocol (P < 0.01) and torque frequency response (P < 0.05) following the high intensity bout. Importantly muscle performance remained reduced 1 h following high intensity exercise but was recovered following low intensity exercise. Muscle function was significantly reduced following higher intensity intermittent exercise in comparison to lower intensity exercise even when the average overall intensity was the same. This study is the first to demonstrate the sensitivity of muscle contractile characteristics to different exercise intensities and the impact of higher intensity bursts on muscle performance.

Initiating treadmill training in late middle age offers modest adaptations in Ca2+ handling but enhances oxidative damage in senescent rat skeletal muscle

Aging skeletal muscle shows an increased time to peak force and relaxation and a decreased specific force, all of which could relate to changes in muscle Ca(2+) handling. The purpose of this study was to determine if Ca(2+)-handling protein content and function are decreased in senescent gastrocnemius muscle and if initiating a training program in late middle age (LMA, 29 mo old) could improve function in senescent (34- to 36-mo-old) muscle. LMA male Fischer 344 x Brown-Norway rats underwent 5-7 mo of treadmill training. Aging resulted in a decrease in maximal sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) activity and a decrease in Ca(2+) release rate but no change in Ca(2+) uptake rate. Efficiency of the Ca(2+) pump was increased with age, as was the content of SERCA2a. Training caused a further increase in SERCA2a content. Aging also caused an increase in protein carbonyl and reactive nitrogen species damage accumulation, and both further increased with training. Consistent with the increase in oxidative damage, heat shock protein 70 content was increased with age and further increased with training. Together, these results suggest that while initiating exercise training in LMA augments the age-related increase in expression of heat shock protein 70 and the more efficient SERCA2a isoform, it did not prevent the decrease in SERCA activity and exacerbated oxidative damage in senescent gastrocnemius muscle.

No relationship between enzyme activity and structure of nucleotide binding site in sarcoplasmic reticulum Ca(2+)-ATPase from short-term stimulated rat muscle

AIM

We examined whether structural alterations to the adenine nucleotide binding site (ANBS) within sarcoplasmic (endo) reticulum Ca(2+)-ATPase (SERCA) would account for contraction-induced changes in the catalytic activity of the enzyme as assessed in vitro.

METHODS

Repetitive contractions were induced in rat gastrocnemius by electrical nerve stimulation. Measurements of sarcoplasmic reticulum properties were performed on control and stimulated muscles immediately after or at 30 min after the cessation of 5-min stimulation. In order to examine the properties at the ANBS, the binding capacity of SERCA to fluorescence isothiocyanate (FITC), a competitive inhibitor at the ANBS, was analysed in microsomes.

RESULTS

Short-term electrical stimulation evoked a 23.9% and 32.6% decrease (P < 0.05) in SERCA activity and in the FITC binding capacity, respectively, in the superficial region of the muscle. Whereas SERCA activity reverted to normal levels during 30-min recovery, a restoration of the FITC binding capacity did not occur.

CONCLUSION

The discordant changes between the enzyme activity and the FITC binding suggest that, at least during recovery after exercise, changes in SERCA activity may not correlate closely with structural alterations to the ANBS within the enzyme.

Alterations in in vitro function and protein oxidation of rat sarcoplasmic reticulum Ca2+-ATPase during recovery from high-intensity exercise

The hypothesis tested in this study was that the extent to which sarcoplasmic reticulum (SR) Ca(2+)-ATPase is oxidized would correlate with a decline in its activity. For this purpose, changes in the SR Ca(2+)-sequestering ability and the contents of carbonyl and sulfhydryl groups during recovery after exercise were examined in the superficial portions of vastus lateralis muscles from rats subjected to 5 min running at an intensity corresponding to maximal oxygen uptake (50 m min(-1), 10% gradient). A single bout of exercise elicited a 22.4% reduction (P < 0.05) in SR Ca(2+)-ATPase activity. The decreased activity progressively reverted to normal levels during recovery after exercise, reaching normal levels after 60 min of recovery. This change was paralleled by a depressed SR Ca(2+)-uptake rate, and the proportional alteration in these two variables resulted in no change in the ratio of Ca(2+)-uptake rate to Ca(2+)-ATPase activity. The contents of SR Ca(2+)-ATPase protein and sulfhydryl groups in microsomes were unchanged after exercise and during recovery periods. In contrast, the content of carbonyl groups in SR Ca(2+)-ATPase behaved in an opposite manner to that of SR Ca(2+)-ATPase activity. An approximately 80% augmentation (P < 0.05) in the carbonyl group content occurred immediately after exercise. The elevated carbonyl content decreased towards normal levels during 60 min of recovery. These results are strongly suggestive that oxidation of SR Ca(2+)-ATPase is responsible, at least in part, for a decay in the SR Ca(2+)-pumping function produced by high-intensity exercise and imply that oxidized proteins may be repaired during recovery from exercise.