Resistance exercise protects mice from protein-induced fat accretion.

Low-protein (LP) diets extend the lifespan of diverse species and are associated with improved metabolic health in both rodents and humans. Paradoxically, many athletes and bodybuilders consume high-protein (HP) diets and protein supplements, yet are both fit and metabolically healthy. Here, we examine this paradox using weight pulling, a validated progressive resistance exercise training regimen, in mice fed either an LP diet or an isocaloric HP diet. We find that despite having lower food consumption than the LP group, HP-fed mice gain significantly more fat mass than LP-fed mice when not exercising, while weight pulling protected HP-fed mice from this excess fat accretion. The HP diet augmented exercise-induced hypertrophy of the forearm flexor complex, and weight pulling ability increased more rapidly in the exercised HP-fed mice. Surprisingly, exercise did not protect from HP-induced changes in glycemic control. Our results confirm that HP diets can augment muscle hypertrophy and accelerate strength gain induced by resistance exercise without negative effects on fat mass, and also demonstrate that LP diets may be advantageous in the sedentary. Our results highlight the need to consider both dietary composition and activity, not simply calories, when taking a precision nutrition approach to health.

Protocol for quantifying the in vivo rate of protein degradation in mice using a pulse-chase technique.

The ability to measure the in vivo rate of protein degradation is a major limitation in numerous fields of biology. Here, we present a protocol for quantifying this rate in mice using a pulse-chase technique that utilizes an azide-bearing non-canonical amino acid called azidohomoalanine (AHA). We describe steps for using chow containing AHA to pulse-label the animal's proteome. We then detail the quantification of AHA-labeled proteins in whole-tissue lysates or histological sections using a copper-catalyzed azide-alkyne cycloaddition 'click' reaction. For complete details on the use and execution of this protocol, please refer to Steinert et al. (2023).1.

Weight Pulling: A Novel Mouse Model of Human Progressive Resistance Exercise.

This study describes a mouse model of progressive resistance exercise that utilizes a full-body/multi-joint exercise (weight pulling) along with a training protocol that mimics a traditional human paradigm (three training sessions per week, ~8-12 repetitions per set, 2 min of rest between sets, approximately two maximal-intensity sets per session, last set taken to failure, and a progressive increase in loading that is based on the individual's performance). We demonstrate that weight pulling can induce an increase in the mass of numerous muscles throughout the body. The relative increase in muscle mass is similar to what has been observed in human studies, and is associated with the same type of long-term adaptations that occur in humans (e.g., fiber hypertrophy, myonuclear accretion, and, in some instances, a fast-to-slow transition in Type II fiber composition). Moreover, we demonstrate that weight pulling can induce the same type of acute responses that are thought to drive these long-term adaptations (e.g., the activation of signaling through mTORC1 and the induction of protein synthesis at 1 h post-exercise). Collectively, the results of this study indicate that weight pulling can serve as a highly translatable mouse model of progressive resistance exercise.

A deep analysis of the proteomic and phosphoproteomic alterations that occur in skeletal muscle after the onset of immobilization.

KEY POINTS: A decrease in protein synthesis plays a major role in the loss of muscle mass that occurs in response to immobilization. In mice, immobilization leads to a rapid (within 6 h) and progressive decrease in the rate of protein synthesis and this effect is mediated by a decrease in translational efficiency. Deep proteomic and phosphoproteomic analyses of mouse skeletal muscles revealed that the rapid immobilization-induced decrease in protein synthesis cannot be explained by changes in the abundance or phosphorylation state of proteins that have been implicated in the regulation of translation. ABSTRACT: The disuse of skeletal muscle, such as that which occurs during immobilization, can lead to the rapid loss of muscle mass, and a decrease in the rate of protein synthesis plays a major role in this process. Indeed, current dogma contends that the decrease in protein synthesis is mediated by changes in the activity of protein kinases (e.g. mTOR); however, the validity of this model has not been established. Therefore, to address this, we first subjected mice to 6, 24 or 72 h of unilateral immobilization and then used the SUnSET technique to measure changes in the relative rate of protein synthesis. The result of our initial experiments revealed that immobilization leads to a rapid (within 6 h) and progressive decrease in the rate of protein synthesis and that this effect is mediated by a decrease in translational efficiency. We then performed a deep mass spectrometry-based analysis to determine whether this effect could be explained by changes in the expression and/or phosphorylation state of proteins that regulate translation. From this analysis, we were able to quantify 4320 proteins and 15,020 unique phosphorylation sites, and surprisingly, the outcomes revealed that the rapid immobilization-induced decrease in protein synthesis could not be explained by changes in either the abundance, or phosphorylation state, of proteins. The results of our work not only challenge the current dogma in the field, but also provide an expansive resource of information for future studies that are aimed at defining how disuse leads to loss of muscle mass.

Do exercise-induced increases in muscle size contribute to strength in resistance-trained individuals?

AIM: Previous work in non-resistance-trained individuals has found that an increase in muscle size has no additive effect on changes in strength. However, it is thought that muscle growth is of increased importance for resistance-trained individuals. PURPOSE: Experiment 1: To examine changes in muscle thickness (MT) and one repetition maximum (1RM) strength following 8 weeks of bi-weekly 1RM practice or traditional training. Experiment 2: To determine whether increasing muscle size increases strength potential when followed by 4 weeks of 1RM training. METHODS: Participants performed biceps curls for 8 weeks (Experiment 1). One arm performed 4 sets of as many repetitions as possible with approximately 70% of 1RM (TRAD), and the other arm performed a single 1RM. For experiment 2, both arms trained for muscle size and strength. RESULTS: Experiment 1 (n = 25): for MT, the posterior probabilities favoured the hypothesis that MT changed more in the TRAD condition [mean difference: 50% site 0.15 (-0.09, 0.21) cm; 60% site 0.14 (0.06, 0.23) cm; 70% site 0.17 (0.10, 0.23) cm]. For 1RM strength, each condition changed equivalently. Experiment 2 (n = 18): for MT, the posterior probabilities favoured the hypothesis that MT changed similarly between conditions following a 4-week strength phase. For changes in 1RM strength, the evidence favoured neither hypothesis (i.e. null vs. alternative). Of note, the mean difference between conditions was small [0.72 (4.3) kg]. CONCLUSIONS: 1RM training produces similar increases in strength as traditional training. Experiment 2 suggests that increases in muscle mass may not increase the 'potential' for strength gain.

An examination of changes in muscle thickness, isometric strength and body water throughout the menstrual cycle.

PURPOSE: The purpose of this study was to examine the changes in muscle size and strength throughout the menstrual cycle in females and to compare these values to a control group of time-matched males. METHODS: 12 males and 16 females visited the laboratory on four occasions. Measures of muscle thickness (MTH), isometric strength and body water were taken during the menstrual phase, ovulation phase and luteal phase of the menstrual cycle. Males scheduled their visits based on a mock menstrual cycle. In addition, participants were asked to complete 4 sets of biceps curls to volitional failure in one arm to examine swelling during each visit. RESULTS: For MTH there was no interaction (p = .73); however, there was a main effect for sex with males having higher MTH values compared to females [4.07 (0.67) versus. 2.73 (0.42) cm, (p < .001)] at all time points. For changes in MTH (swelling) there was no interaction (p = .28). However, there was a main effect for sex, with males demonstrating greater changes in MTH compared to females [0.53(0.11) versus. 0.40 (0.10) cm, (p < .001)]. Similarly, for total body water, there was no interaction (p = .66). However, males had greater total body water compared to females [49.6 (6.8) versus. 32.3(3.9) kg, p < .001)] at all time points. Finally, for isometric strength, there was no interaction (p = .23). However, there was a main effect for sex. Males had higher isometric strength values compared to females [285 (42) versus. 156(36) N (p < .001)]. CONCLUSIONS: Phase of the menstrual cycle does not appear to influence MTH, isometric strength or total body water.

An examination of changes in skeletal muscle thickness, echo intensity, strength and soreness following resistance exercise.

It is suggested that changes in echo intensity (EI) measured through ultrasound can detect muscle swelling. However, changes in EI have never been examined relative to a non-exercise control following naïve exposure to exercise. PURPOSE: Examine the changes in muscle thickness (MT), EI and isometric strength (ISO) before, immediately after, and 24, and 48 hr following biceps curls. METHODS: Twenty-seven non-resistance-trained individuals visited the laboratory four times. During visit 1, paperwork was completed and strength was measured. During visit 2, MT and ISO were measured before four sets of curls. Additional measures were taken immediately after exercise, as well as 24 and 48 hr post. Results are displayed as means (SD). RESULTS: For MT, there was an interaction (p < .001). For the experimental condition, MT increased from pre [2.88(0.64) cm] to post [3.27(0.67) cm] and remained elevated 48 hr post. There were no changes for MT in the control arm. In the experimental arm, EI increased from pre [22.9(9.6) AU] to post [29.1(12.3) AU] exercise and returned to baseline by 24 hr. For the control condition, EI was different between pre [24.8(10.2) AU] and 48 hr [21.5(10.7) AU]. The change in EI in the experimental condition was greater than the control condition immediately post (p = .039) and at 48 hr (p = .016). For ISO, there was an interaction (p < .001). In the experimental condition, ISO decreased from pre [40.6(14.7) Nm)] to post [24.8(9.4) Nm] and remained depressed. CONCLUSIONS: Exercise produced a swelling response, which was elevated 48 hr post. Despite a sustained increase in MT, EI was only elevated immediately post exercise.

Cardiovascular and Muscular Response to NO LOAD Exercise with Blood Flow Restriction.

Changes in muscle thickness (MT), isometric torque, and arterial occlusion pressure (AOP) were examined following four sets of twenty unilateral elbow flexion exercise. Participants performed four sets of maximal voluntary contractions with no external load throughout a full range of motion of a bicep curl with and without the application of blood flow restriction (BFR). For torque there was an interaction (p = 0.012). The BFR condition had lower torque following exercise (56.07 ± 17.78 Nm) compared to the control condition (58.67 ± 19.06 Nm). For MT, there was a main effect for time (p < 0.001). MT increased from pre (3.52 ± .78cm) to post (3.68 ± 81cm) exercise and remained increased above baseline 15 min post-exercise. For AOP, there was an interaction (p = 0.027). The change in AOP was greater in the BFR condition (16.6 ± 13.42mmHg) compared to the control (11.1 ± 11.84 mmHg). NO LOAD exercise with BFR let to greater reductions in torque and an exaggerated cardiovascular response compared to exercise alone. There were no differences in swelling. These results suggest that the application of BFR to NO LOAD exercise may result in greater fatigue.