Time Course Evaluation of Mitogen-Activated Protein Kinase Phosphorylation to Resistance Exercise: A Systematic Review.

ABSTRACT: Lee, CJ and Nicoll, JX. Time course evaluation of mitogen-activated protein kinase phosphorylation to resistance exercise: a systematic review. J Strength Cond Res 37(3): 710-725, 2023-Resistance exercise (RE) can increase the signaling activities of mitogen-activated protein kinases (MAPKs), specifically extracellular signal-regulated kinases 1/2 (ERK1/2), p90 ribosomal S6 kinases (p90RSK), c-Jun NH2-terminal kinases (JNK), and p38-MAPK. These RE-induced responses contribute to various intracellular processes modulating growth and development in skeletal muscles, playing an essential role in resistance training adaptations. The time course of MAPK phosphorylation to different RE conditions, such as training experience and varying loads, remains ambiguous. A systematic review was conducted to determine the effects of different post-RE recovery time points on the MAPK signaling cascade. In addition, the effects of loading and training statuses on MAPK responses were also investigated. The review was performed according to the preferred reporting items for systematic reviews and meta-analyses guidelines with a literature search incorporating 3 electronic databases. A modified version of the Downs and Black checklist was used to evaluate the methodological quality of the studies. The signaling responses were measured within a time range between immediately post-RE and >6 hours post-RE. Forty-four studies met the inclusion criteria, and all were classified as good-to-moderate methodological quality. Mitogen-activated protein kinase phosphorylation increased to different levels after RE, with the highest near the cessation of exercise. Although overall signaling was attenuated among trained individuals likely because of training adaptations, greater MAPK responses can be attributed to moderate loads of 65-85% 1RM regardless of the training experience. However, specific training-induced responses remain equivocal, and further investigations are required to determine the ideal training parameters to optimize anabolic intramuscular signaling, which may likely optimize resistance training adaptations.

The effects of a caffeine containing pre-workout supplement on ß2-adrenergic and MAPK signaling during resistance exercise.

AIM: The acute myocellular responses of caffeine supplementation during resistance exercise (RE) have not been investigated. ß2-Adrenergic receptors (ß2AR) may be a target of the stimulatory effects of caffeine and stimulate bioenergetic pathways including protein kinase A (PKA), and mitogen-activated protein kinases (MAPK). PURPOSE: Elucidate the effects of pre-workout supplementation on signaling responses to an acute RE bout. METHODS: In a randomized, counter-balanced, double-blind, placebo-controlled, within-subject crossover study, ten resistance-trained males (mean ± SD; age = 22 ± 2.4 years, height = 175 ± 7 cm, body mass = 84.1 ± 11.8 kg) consumed a caffeine containing multi-ingredient pre-workout supplement (SUPP) or color and flavor matched placebo (PL) 60 min prior to an acute RE bout of barbell back squats. Pre- and post-exercise muscle biopsies were analyzed for the phosphorylation (p-) of ß2AR, PKA, and MAPK (ERK, JNK, p38). Epinephrine was determined prior to supplementation (baseline; BL), after supplementation but prior to RE (PRE), and immediately after RE (POST). RESULTS: Epinephrine increased at PRE in SUPP (mean ± SE: 323 ± 34 vs 457 ± 68 pmol/l; p = 0.028), and was greatest at POST in the SUPP condition compared to PL (5140 ± 852 vs 2862 ± 498 pmol/l; p = 0.006). p-ß2AR and p-MAPK increased post-exercise (p < 0.05) with no differences between conditions (p > 0.05). Pearson correlations indicated there was a relationship between epinephrine and p-ß2AR in PL (r = - 0.810; p = 0.008), and p-ß2AR and ERK in SUPP (r = 0.941; p < 0.001). CONCLUSION: Consumption of a caffeine containing pre-workout supplement improves performance, possibly through increases in pre-exercise catecholamines. However, the acute myocellular signaling responses were largely similar post-exercise.

Intramuscular hyaluronic acid expression following repetitive power training induced nonfunctional overreaching.

Hyaluronic acid (HA) contributes to extracellular matrix viscosity and fiber regeneration. HA role in resistance training (RT) performance adaptations is unclear. RT men performed power training (nonfunctional overreaching (NFOR) or normal training (CG)) over 7.5 days. Post RT, the CG improved power while NFOR did not with HA content decreasing 34.5% in NFOR with no change in CG. HA is critical for muscular recovery; decreased HA may contribute to impaired power adaptations with NFOR RT. Novelty: Nonfunctional over-reaching decreases muscular hyaluronic acid.

Androgen and glucocorticoid receptor phosphorylation following resistance exercise and pre-workout supplementation.

PURPOSE: Consumption of caffeine or caffeine containing pre-workout supplements (SUPP) augments steroid hormone responses to resistance exercise (RE). However, the activation of glucocorticoid (GR) and androgen receptors (AR) following RE SUPP has not been investigated. The purpose of this study was to determine the influence of a pre-workout supplement on AR and GR phosphorylation following RE. METHODS: In a randomized, counter-balanced, double-blind, placebo-controlled, within-subject crossover study, ten resistance-trained males ((X¯±SD, age = 22 ± 2.4 yrs, hgt = 175 ± 7 cm, body mass = 84.1 ± 11.8 kg) performed four sets of 8 repetitions of barbell back squats at 75% of their 1-repetition maximum (1-RM) with two minutes of rest between sets and a fifth set of barbell back squats at 60% of 1-RM until concentric failure. A SUPP or flavor and color matched placebo (PL) was consumed 60-minutes prior to RE. Vastus lateralis muscle biopsies were obtained prior to supplementation at rest (BL), and ten minutes post-exercise (POST). Biopsies were analyzed for phosphorylated GR (ser134, ser211, and ser226) and phosphorylated AR (ser81, ser213, ser515, ser650) via western blotting. RESULTS: pGRser134 decreased, and pGRser226 increased following RE (p < 0.05) with no difference between conditions (p > 0.05). pGRser211 was unchanged after RE (p > 0.05). pARser515 increased, and total AR expression decreased after RE (p < 0.05) in SUPP only. Testosterone and cortisol were not different between SUPP and PL at POST (p > 0.05). CONCLUSION: RE influences AR and GR phosphorylation, and SUPP minimally influences this response in the early recovery period.

MAPK, androgen, and glucocorticoid receptor phosphorylation following high-frequency resistance exercise non-functional overreaching.

PURPOSE: Stressful training with insufficient recovery can impair muscle performance. Expression of mitogen-activated protein kinases (MAPK) has been reported at rest following overreaching and overtraining. The acute myocellular exercise response to stressful training with insufficient recovery has not been investigated. We investigated MAPK, androgen, and glucocorticoid receptor phosphorylation following a period of stressful training. METHODS: Sixteen resistance-trained men were matched on barbell squat 1 repetition maximum strength and randomized into a group that performed normal training or stressful training with insufficient recovery. The control group (CON) performed three speed-squat training sessions on non-consecutive days, while the stressful training group (NFOR) performed 15 training sessions over 7.5 days. Resting and post-exercise skeletal muscle biopsies were obtained prior to (T1) and after the training period (T2). Samples were analyzed for total and phosphorylated androgen receptor (AR), glucocorticoid receptor (GR), and MAPKs (ERK, JNK, and p38). RESULTS: Total AR were down-regulated post-exercise at T2 in NFOR only. Phospho-AR at ser515 increased in both groups post-exercise at T1; however, ser515 only increased at T2 in NFOR. Phosphorylated ERK, JNK, and p38 increased post-exercise in CON and NFOR at T1 and T2. Post-exercise phospho-p38 was blunted in NFOR at T2 compared to T1. After the training intervention, resting phospho-p38 was higher in NFOR compared to T1. At T2, post-exercise phospho-GR at ser226 was lower compared to T1, and resting levels increased in NFOR. CONCLUSION: Steroid receptors are phosphorylated after acute resistance exercise, and in addition to MAPKs, are differentially regulated after stressful training with insufficient recovery.

Skeletal muscle signaling responses to resistance exercise of the elbow extensors are not compromised by a preceding bout of aerobic exercise.

The current study examined the effects of a preceding bout of aerobic exercise (AE) on subsequent molecular signaling to resistance exercise (RE) of the elbow extensors. Eleven men performed unilateral elbow-extensor AE (~45 min at 70% peak workload) followed by unilateral RE (4 × 7 maximal repetitions) for both arms. Thus, one arm performed AE+RE interspersed with 15 min recovery, whereas the other arm conducted RE alone. Muscle biopsies were taken from the triceps brachii of each arm immediately before (PRE) and 15 min (POST1) and 3 h (POST2) after RE. Molecular markers involved in translation initiation, protein breakdown, mechanosignaling, and ribosome biogenesis were analyzed. Peak power during RE was reduced by 24% (±19%) when preceded by AE (P < 0.05). Increases in PGC1a and MuRF1 expression were greater from PRE to POST2 in AE+RE compared with RE (18- vs. 3.5- and 4- vs. 2-fold, respectively, interaction, P < 0.05). Myostatin mRNA decreased in both arms (P < 0.05). Phosphorylation of AMPK (Thr172) increased (2.5-fold), and 4E-BP1 (Thr37/46) decreased (2.0-fold), after AE (interactions, P < 0.05). p70 S6K, yes-associated protein, and c-Jun NH2-terminal kinase phosphorylation were unaltered, whereas focal adhesion kinase decreased ~1.5-fold, and ß1-integrin increased ~1.3- to 1.5-fold, (time effect, P < 0.05). Abundance of 45S pre-ribosomal (r)RNA (internally transcribed spacer, ITS) decreased (~30%) after AE (interaction, P < 0.05), whereas CMYC mRNA was greater in AE+RE compared with RE (12-fold, P < 0.05). POLR1B abundance increased after both AE+RE and RE. All together, our results suggest that a single bout of AE leads to an immediate decrease in signaling for translation initiation and ribosome biogenesis. Yet, this did not translate into altered RE-induced signaling during the 3-h postexercise recovery period.

Effects of Different Athletic Playing Surfaces on Jump Height, Force, and Power.

Hatfield, DL, Murphy, KM, Nicoll, JX, Sullivan, WM, and Henderson, J. Effects of different athletic playing surfaces on jump height, force, and power. J Strength Cond Res 33(4): 965-973, 2019-Artificial turfs (ATs) have become more commonplace. Some aspects of performance such as speed seem to be better on ATs, but there are few published studies on the effects of playing surfaces on performance. Furthermore, there is no research that compares performance on ATs, hard surfaces (HSs), and different composite natural surfaces. Forty-three subjects, 21 men (age: 20 ± 1.82 years; height: 177.53 ± 5.87 cm; body mass: 78.44 ± 11.59 kg; and body fat: 11.17 ± 4.45%) and 22 women (age: 25 ± 1.32 years; height: 161.37 ± 6.47 cm; body mass: 60.94 ± 10.24 kg; and body fat: 27.16 ± 7.08%) performed a single countermovement jump (SCMJ), repeated CMJs (RCMJs), and single depth jump (SDJ) on 4 different playing surfaces (peat soil composition turf [NT1], sandy loam composition turf [NT2], 1 AT, and 1 HS. Repeated-measures analysis of variance with Bonferroni post hoc was used to calculate differences in performance across playing surfaces. Statistical significance was set at p ≤ 0.05. Force and jump height were not different across different surfaces. Men had significantly higher force, power, and jump height on all surfaces. Only SCMJ power was lower on NT1 compared with all other surfaces. The difference in power between surfaces was not reproduced when RCMJ and SDJ were performed, and may be due to the increased reactiveness of the stretch-shortening cycle during those jumps. Because of marginal differences between athletic performance and playing surface type, future research comparing playing surface type and other aspects of athletic success such as rate of injury should be considered.

The skeletal muscle fiber: a mechanically sensitive cell.

The plasticity of skeletal muscle, whether an increase in size, change in metabolism, or alteration in structural properties, is in a continuous state of flux largely dependent upon physical activity. Much of the past research has expounded upon these ever-changing aspects of the muscle fiber following exercise. Specifically, endocrine and paracrine signaling have been heavily investigated lending to much of the past literature comprised of such endocrinological dynamics following muscle activity. Mechanotransduction, the ability of a cell to convert a mechanical stimulus into an intracellular biochemical response, has garnered much less attention. Recent work, however, has demonstrated the physical continuity of the muscle fiber, specifically demonstrating a continuous physical link between the extracellular matrix (ECM), cytoskeleton, and nuclear matrix as a means to rapidly regulate gene expression following a mechanical stimulus. Similarly, research has shown mechanical stimuli to directly influence cytoplasmic signaling whether through oxidative adaptations, increased muscle size, or enhanced muscle integrity. Regrettably, minimal research has investigated the role that exercise may play within the mechanotransducing signaling cascades. This proposed line of study may prove paramount as muscle-related diseases greatly impact one's ability to lead an independent lifestyle along with contributing a substantial burden upon the economy. Thus, this review explores both biophysical and biochemical mechanotransduction, and how these signaling pathways may be influenced following exercise.

Effect of Three Different Maximal Concentric Velocity Squat Protocols on MAPK Phosphorylation and Endocrine Responses.

Kudrna, RA, Fry, AC, Nicoll, JX, Gallagher, PM, and Prewitt, MR. Effect of three different maximal concentric velocity squat protocols on MAPK phosphorylation and endocrine responses. J Strength Cond Res 33(6): 1693-1703, 2019-The purpose of this study was to determine the effect of 3 different back squat protocols on intracellular signaling, endocrine responses, and power fatigue. Nine recreationally trained men (X ± SD; age: 21.4 ± 0.6 years; height: 177.8 ± 5.1 cm; body mass: 78.7 ± 9.7 kg), completed 3 maximal concentric velocity squat protocols in a randomized order. Testing protocols consisted of 5 sets of 10 repetitions at 30% of 1 repetition maximum (1RM); 5 sets of 5 repetitions at 70% of 1RM; and 5 sets of 3 repetitions at 90% of 1RM. Average system power for each set was obtained using a tethered external dynamometer. Pre-exercise and postexercise blood draws were analyzed for lactate, testosterone, human growth hormone (hGH), and cortisol. Muscle biopsies assessed pre-exercise and postexercise extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 phosphorylation using western blotting. Cortisol, hGH, and lactate increased after exercise (p ≤ 0.05), but did not differ between protocols (p > 0.05). Testosterone was unaltered (p > 0.05). Average power was lower for the 90% protocol than for the 30% protocol across all sets (p < 0.01). Average power was lower after the fourth and fifth set compared with the first and second set in the 90% protocol only (p ≤ 0.05). The ratio of phosphorylated-to-total ERK1/2 was higher postexercise after 90% protocol only (p ≤ 0.05). The ratio of phosphorylated-to-total p38 was unaltered after exercise (p > 0.05). Resistance load seems to affect power fatigue across the 5 sets of resistance exercise. This study found modest changes in ERK1/2 and no changes in p38 phosphorylation after maximal concentric velocity squats. Exercise volume, modality, and training status of subjects may account for these findings.

Sex-based differences in resting MAPK, androgen, and glucocorticoid receptor phosphorylation in human skeletal muscle.

PURPOSE: To determine if there is differential expression and phosphorylation of the androgen receptor (AR), glucocorticoid receptor (GR), and mitogen-activated protein kinases (MAPK) in skeletal muscle at rest between males and females. METHODS: Ten college-aged males (mean ±â€¯SD; age = 22 ±â€¯2.4 yrs, ht = 175 ±â€¯7 cm, body mass = 84.1 ±â€¯11.8 kg) and ten females (mean ±â€¯SD; age = 20 ±â€¯0.9 yrs; ht = 169 ±â€¯7 cm; body mass = 67.1 ±â€¯8.7 kg) reported to the laboratory following an overnight fast. Resting muscle biopsies were collected from the vastus lateralis and analyzed for total and phosphorylated GR (ser134, ser211, and ser226), total and phosphorylated AR (ser81, ser213, ser515, ser650), and total and phosphorylated MAPK (ERK, JNK, p38) via western blotting. A phosphorylation index (PI) was calculated to determine phosphorylated receptor expression after accounting for differences in total receptor content. RESULTS: Males had more total AR compared to females (+42 ±â€¯4%; p < 0.001). Females had higher phosphorylation of ARser81 (+87 ±â€¯11%; p = 0.001) and ser515 (+55 ±â€¯13%; p = 0.019). However, when the phosphorylated ratios were corrected for differences in total AR expression (i.e. our PI), the overall phosphorylation at these sites were similar between sexes (ser515, males = 100% vs females 92%; ser81, males = 100% vs females = 107%). pGRser134 was higher in males compared to females (+50 ±â€¯15%; p = 0.016). Phospho-p38 was higher in females compared to males (+5050 ±â€¯16%; p < 0.001). CONCLUSION: At rest, ARs and GRs are differentially phosphorylated at some, but not all sites when comparing males and females. Differential regulation of phosphorylated AR, GR, and p38 between males and females may have implications for the degree of muscle adaptations observed following resistance or endurance training.

Thyroid hormones and commonly cited symptoms of overtraining in collegiate female endurance runners.

PURPOSE: Overtraining syndrome (OTS) is reported in endurance sports. Thyroid hormones (TH) regulate metabolism, mood, and energy production, and may play a role in OTS of endurance athletes. The purpose of this study was to investigate relationships in TH and symptoms of OTS in track and field endurance runners (ER). METHODS: Sixteen female track and field middle distance (MD; n = 9; age: 20.2 ± 1.5 years; ht: 167.86 ± 5.04 cm; body-mass: 57.97 ± 5.05 kg; VO2MAX: 53.62 ± 6.04 ml/kg/min) and long distance (LD; n = 7; age: 20.5 ± 1.5 years; ht: 162.48 ± 6.11 cm; body-mass: 56.15 ± 5.99 kg; VO2MAX: 61.94 ± 3.29 ml/kg/min) ER participated in this descriptive study (15-weeks). Thyroid-stimulating hormone (TSH), triiodothyronine (T 3), and thyroxine (T 4), were collected at pre-(PRE) and post-season (POST). A fatigue scale was administered weekly, and percent change (PΔ) in race time (season best vs. championship performance) was calculated. Wilcoxon-sign ranked tests and Spearman's rho correlations were used to determine changes and relationships between TH and performance. RESULTS: TSH, T 3 and T 4 did not change from PRE to POST. The percent change (PΔ) in T 3 from PRE to POST was correlated with running performance at the end of the season (ρ = - 0.70, p = 0.036). Fatigue at week 12 correlated with running performance at the end of the season (ρ = - 0.74, p = 0.004). CONCLUSION: TH may be valuable in assessing the overall training state of ER. TH concentrations change too slowly to be a frequent marker of monitoring OTS, but are related to markers of decreased performance. Monitoring dietary intake, and fatigue may be predictive markers to assess OTS and training status of female ER.

Resting MAPK expression in chronically trained endurance runners.

PURPOSE: There is a paucity of research investigating the expression of mitogen-activated protein kinases (MAPK) in chronically trained (CT) athletes. Thus, it is unclear how MAPK may contribute to performance and muscle adaptation in CT subjects. The purpose of this study was to determine MAPK total protein, and phosphorylated expression of extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun N-terminal kinase (JNK), and p38-MAPK (p38) between untrained, and chronically trained runners. METHODS: Tissue samples were analysed from sedentary (SED; n = 5) controls and chronically trained runners (CT; n = 5). Resting muscle biopsy samples were analysed for total-MAPK - and ratio of phosphorylated/total (p-MAPK) - ERK1/2, JNK, and p38-MAPK via western blotting. Mann-Whitney U tests and effect sizes were utilized to determine differences in total MAPK protein content and phosphorylation status between SED and CT subjects. RESULTS: There was no difference in total-MAPK expression between SED and CT (p > .05). p-p38-MAPK tended to be greater for CT compared to SED (p = .07). There were moderate effect sizes of decreased pERK/total-ERK (d = -0.69) and increased pJNK/total-JNK (d = 0.54) in CT compared to SED. There was a positive correlation between p-p38-MAPK/total-MAPK and the percentage of type I fibres (r = 0.73, p = .016). CONCLUSION: Contrary to previous studies, chronic endurance training does not greatly influence total MAPK protein expression in chronically trained runners. However, resting phosphorylation of p38-MAPK may contribute to enhanced oxidative metabolism at chronically trained levels. These alterations are likely involved in the different physiological adaptations that occur following long-term training or at highly competitive levels.

Noninvasive Assessment of Skeletal Muscle Myosin Heavy Chain Expression in Trained and Untrained Men.

Fry, AC, Housh, TJ, Cramer, JB, Weir, JP, Beck, TW, Schilling, BK, Miller, JD, and Nicoll, JX. Noninvasive assessment of skeletal muscle myosin heavy chain expression in trained and untrained men. J Strength Cond Res 31(9): 2355-2362, 2017-Numerous conditions and types of physical activity (e.g., exercise, aging, and muscle-related diseases) can influence muscle fiber types and the proteins expressed. To date, muscle fibers can only be characterized by actually obtaining a tissue sample using the invasive muscle biopsy procedure. Mechanomyography (MMG) is the assessment of the vibration properties of contracting skeletal muscle and has been proposed as a possible noninvasive method for muscle fiber analysis. Therefore, the purpose of this project was to examine the feasibility of using MMG and muscle performance measures to noninvasively assess muscle fiber characteristics. Fifteen men (5 endurance-trained, 5 weight-trained, and 5 sedentary) provided muscle samples from their vastus lateralis muscle. These samples were analyzed for relative myosin heavy chain (MHC) protein expression, which is highly correlated with % muscle fiber type areas. Additionally, each subject performed several muscle performance tests, and MMG of the quadriceps was assessed during a knee extension exercise. Multiple regression was used to develop prediction equations for determining relative muscle content of MHC types I, IIa, and IIx. A combination of MMG and knee extension performance variables estimated types I, IIa, and IIx MHCs with approximately 80% accuracy. Although preliminary, these data suggest that muscle performance tests in addition to MMG assessments during a simple muscle performance task (knee extension) can be used to estimate muscle fiber type composition in a healthy male population. Such methods could ultimately be used to noninvasively monitor muscle health and fitness.

Age-related differences in twitch properties and muscle activation of the first dorsal interosseous.

OBJECTIVE: To examine twitch force potentiation and twitch contraction duration, as well as electromyographic amplitude (EMGRMS) and motor unit mean firing rates (MFR) at targeted forces between young and old individuals in the first dorsal interosseous (FDI). Ultrasonography was used to assess muscle quality. METHODS: Twenty-two young (YG) (age=22.6±2.7years) and 14 older (OD) (age=62.1±4.7years) individuals completed conditioning contractions at 10% and 50% maximal voluntary contraction, (MVC) during which EMGRMS and MFRs were assessed. Evoked twitches preceded and followed the conditioning contractions. Ultrasound images were taken to quantify muscle quality (cross-sectional area [CSA] and echo intensity [EI]). RESULTS: No differences were found between young and old for CSA, pre-conditioning contraction twitch force, or MFRs (P>0.05). However, OD individuals exhibited greater EI and contraction duration (P<0.05), and EMGRMS (YG=35.4±8.7%, OD=43.4±13.2%; P=0.034). Twitch force potentiation was lower for OD (0.311±0.15N) than YG (0.619±0.26N) from pre- to post-50% conditioning contraction (P<0.001). CONCLUSIONS: Lower levels of potentiation with elongated contraction durations likely contributed to greater muscle activation during the conditioning contractions in the OD rather than altered MFRs. Ultrasonography suggested age-related changes in muscle structure contributed to altered contractile properties in the OD. SIGNIFICANCE: Greater muscle activation requirements can have negative implications on fatigue resistance at low to moderate intensities in older individuals.

Changes in resting mitogen-activated protein kinases following resistance exercise overreaching and overtraining.

PURPOSE: Many physiological maladaptations persist after overreaching and overtraining resistance exercise (RE). However, no studies have investigated changes in mitogen-activated protein kinases (MAPK) after overtraining in humans, despite their critical role regulating exercise-induced muscular adaptations. The purpose of this study was to describe the changes in total and resting phosphorylation status of extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun NH2-terminal kinase (JNK) and p38-MAPK following a period of RE overreaching or overtraining. METHODS: Following 2-4 weeks of normal training (low volume/low intensity), two groups of males performed either a high-power overreaching protocol (HPOR n = 6, mean ± SD, age 23 ± 3.4 years, mass 86.5 ± 17.7 kg, height 1.77 ± 0.06 m) or high-intensity overtraining protocol (HIOT n = 8, age 19.8 ± 1.8 years, mass 76.8 ± 6.7 kg, height 1.8 ± 0.06 m). Resting muscle biopsies were obtained at baseline (BL; end of normal training period) and 24 h after the final session of stressful training (i.e., HPOR or HIOT programs). Total MAPK and ratio of phosphorylated/total (p-MAPK)- ERK1/2, JNK, and p38-MAPK were analyzed via western blotting. 2 × 2 (group × time) ANOVA determined differences in MAPK between BL and post-training protocols. RESULTS: Compared to BL, total-ERK increased after HPOR, but decreased after HIOT (p ≤ 0.05). p-ERK1/2/total-ERK increased after HIOT (p ≤ 0.05). The ratio of p-JNK/total-JNK and p-ERK1/2/total-ERK decreased after HPOR (p ≤ 0.05); however, this result was primarily due to increased total MAPK content. p-p38-MAPK decreased after HPOR (p ≤ 0.05). CONCLUSION: Total and p-MAPK are differentially expressed after HPOR and HIOT RE. These changes are likely involved in the maladaptation reported in overreaching and overtraining exercise. This is the first study describing altered MAPK in RE overtrained and overreached humans.

Resting extracellular signal-regulated protein kinase 1/2 expression following a continuum of chronic resistance exercise training paradigms.

Extracellular signal-regulated protein kinase 1/2 (ERK1/2) moderates skeletal muscle growth; however, chronic responses of this protein to unique resistance exercise (RE) paradigms are yet to be explored. The purpose of this investigation was to describe the long-term response of ERK1/2 following circuit weight training (CWT), recreationally weight training (WT), powerlifting (PL) and weightlifting (WL). Independent t-tests were used to determine differences in trained groups compared to sedentary controls. Total ERK1/2 content was lower in PL and WL compared to their controls (p ≤ 0.05). Specific trained groups displayed large (WL: pERK/total-ERK; d = 1.25) and moderate (CWT: total ERK1/2; d = 0.54) effect sizes for altered kinase expression compared to controls. The results indicate ERK1/2 expression is down-regulated after chronic RE in well-trained weightlifters and powerlifters. Lower expression of this protein may be a method in which anabolism is tightly regulated after many years of high-intensity RE.

Effects of Circadian Rhythm on Power, Force, and Hormonal Response in Young Men.

Circadian rhythms (CRs) persist in many physiological systems related to performance. The effects of circadian patterns on dynamic muscular power are minimal and conflicting. Furthermore, no study to date has investigated the effect of CR on bench press throws (BPTs) despite its popularity as a modality to increase muscular power. The purpose of this study was to examine the effects of circadian variations on muscular power output and hormonal changes in men. College aged men (n = 7, age: 23.6 ± 1.3 years, height: 179.9 ± 5.4 cm, and body mass: 81.5 ± 19.7 kg.) were recruited for this repeated measures study. Testing occurred at 4 different times of day (04:00, 10:00, 16:00, and 22:00 hours). Testosterone (T) and cortisol (C) hand dynamometer strength (GS), heart rate (HR), mental readiness (MR), BPT and squat jumps (SJs), power (P), and force (F) were measured at each time point. Statistical significance was set at (p ≤ 0.05). There were no significant differences in HR, MR, and GS among all time points. There were no decrements in P or F in BPT or SJ among any time point (p ≥ 0.05). Testosterone and C decreased significantly throughout the day (p ≤ 0.05). Although P and F output differed at various percentages of 1 repetition maximum, they were not affected by circadian pattern, such that muscular performance was not impaired at any time point. Practical implications of these data indicate that high force and power exercises using BPT or SJ may be performed any time of day without detrimental decreases in acute performance.

Muscular Strength and Power in 3-to 7-Year-Old Children.

To determine absolute and relative (adjusted for body mass) strength, mean power, and mean velocity for upper and lower body resistance exercises, forty-seven young boys and girls participated in maximal strength testing. Healthy young boys and girls, ages 3- to 7-years old, were tested for one-repetition maximum (1-RM) strength, and 70% of 1-RM to determine mean power and mean velocity on the chest press and leg press exercises. Adult weight machines were modified to accommodate the smaller size and lower strength levels of the children. A 2 × 4 (sex × age) ANOVA was used to determine age and sex differences in performance. No interaction or sex differences were observed for any variable at any age. 1-RM strength, mean power, and mean velocity significantly increased across ages (p ≤ .05). When adjusted for body mass, the changes were insignificant, with one exception. Relative mean power for the bench press increased with age. Data indicated children from 3-7 years of age are capable of performing strength and power tests, but may require more attempts at maximal loads compared with adults. It appears that muscular strength and velocity during this stage of development are primarily dependent on increasing body mass, whereas power is influenced by additional variable(s).