Changes in physical performance, body composition and physical training during military operations: systematic review and meta-analysis.

Systematic review and meta-analysis applying PRISMA guidelines with a PICOS format was constructed to provide an overview of changes in physical performance, body composition and physical training in soldiers during prolonged (≥ 3 months) military operations. Twenty-four studies out of the screened 4431 records filled the inclusion criteria. A small decrease in endurance performance was the most consistent finding (Hedge's g [g] - 0.21, 95% CI - 0.01 to - 0.41) while small overall increases in maximal strength of the lower (g 0.33, 95% CI 0.16-0.50) and upper body (g 0.33, 95% CI 0.19-0.46) were observed. In addition, small increases in strength endurance (push-up, g 0.34, 95% CI 0.15-0.52; sit-up g 0.26, 95% CI 0.07-0.44) were observed. The overall changes in body composition were trivial. Heterogeneity in the outcome variables varied mainly between low to moderate. Large inter-individual variations were observed in physical training volume, including decrements especially in endurance training frequency and volume. A reduction in total training load was often associated with negative changes in body composition and physical performance according to the principle of training specificity. Individuals with higher initial fitness level were more susceptible to decrements in their physical performance during operation.

Sex differences in musculoskeletal injury epidemiology and subsequent loss of tactical readiness during Marine Corps Officer Candidates School.

INTRODUCTION: The US Marine Corps (USMC) Officer Candidates School (OCS) is a 10-week training course for Marine Officer Candidates (MOCs). OCS training is rigorous and demanding, which results in a high risk of musculoskeletal injuries (MSIs). The objective of this analysis was to describe MSIs among women and men during the USMC OCS at Quantico, Virginia, from September 2020 to November 2021. METHODS: This prospective cohort study assessed MSIs that occurred among 736 MOCs (women: 17.8% of sample, men: 82.2%). Data for the study were derived from routinely collected injury data by athletic trainers and physical therapists embedded within the training units. Injury incidence, event at the time of injury occurrence, anatomic location, injury type and disposition following injury were described. Fisher's exact tests were used to compare proportions of injured women and men. RESULTS: The cumulative injury incidence was higher among women (39.7%) compared with men (23.1%, p<0.001). When specific events associated with injuries were reported, most frequent events were the obstacle course (women: 20.9% of injuries, men: 12.9%) and the conditioning hike (women: 11.6%, men: 6.9%). Most injures affected the lower body (women: 67.4%, men: 70.8%). The most frequent body part injured was the lower leg (18.6%) in women and the knee (23.3%) in men. The most frequent injury type was strain (women: 39.5%, men: 24.3%), followed by sprain (women: 16.3%, men: 14.9%). A greater percentage of female (92.3%) compared with male MOCs (69.3%; p<0.001) were assigned light duty status following MSIs. CONCLUSIONS: Mitigation of injuries during OCS events such as the obstacle course and the conditioning hike needs further investigation. The high risk of overuse lower leg injuries among women and the higher incidence of injuries among women compared with men underscore the need for further investigation of modifiable sex-specific injury risk factors.

Aerobic fitness predicted by demographics, anthropometrics, health behaviour, physical activity and muscle fitness in male and female recruits entering military service.

INTRODUCTION: The physical and mental training load can be high during military service. Therefore, tailored preconditioning programmes based on assessment of physical fitness could increase readiness for military service, especially among those ones with lower baseline fitness level. The purpose of present study was to investigate how self-assessed health behaviour, physical activity and muscle fitness can predict physical fitness in young male and female military cohorts. METHODS: Demographics, health behaviour and daily physical activity preceding military service were surveyed by a questionnaire. Thereafter, physical fitness was assessed during the military service by the tests of 12 min running, 1 min push-ups and sit-ups. Explosive power of the lower extremities was studied by maximal standing long jump. Measurements of body anthropometry consisted of body mass, height, and waist circumference. RESULTS: The two strongest individual predictors of objectively measured running distance in 12 min were self-reported physical activity and physical readiness in both men and women. Self-reported physical activity, readiness for military service, sitting time, education, smoking and body anthropometrics together explained 52% of the variance in the 12 min running test result (R2=0.52, mean absolute percentage error (MAPE) 8.8%, mean absolute error (MAE) 207 m) in men, while for women the predictive values were weaker. Addition of muscle fitness results to the adjusted regression model further improved the model, which explained 59% of the variance in the 12 min running tests result of male conscripts (R2=0.59, MAPE 7.8%, MAE 181 m). CONCLUSION: In the present study, self-reported physical activity, muscle fitness, physical readiness for military service, sitting time, education, smoking and body anthropometrics predicted inadequately the measured endurance capacity among recruits. The present questionnaire-based variables do not accurately predict physical fitness of recruits and thus, they are not either suitable for practical use for preconditioning programmes or preselection before entering the military service.

Use-dependent corticospinal excitability is associated with resilience and physical performance during simulated military operational stress.

Simulated military operational stress (SMOS) provides a useful model to better understand resilience in humans as the stress associated with caloric restriction, sleep deficits, and fatiguing exertion degrades physical and cognitive performance. Habitual physical activity may confer resilience against these stressors by promoting favorable use-dependent neuroplasticity, but it is unclear how physical activity, resilience, and corticospinal excitability (CSE) relate during SMOS. To examine associations between corticospinal excitability, physical activity, and physical performance during SMOS. Fifty-three service members (age: 26 ± 5 yr, 13 women) completed a 5-day and -night intervention composed of familiarization, baseline, SMOS (2 nights/days), and recovery days. During SMOS, participants performed rigorous physical and cognitive activities while receiving half of normal sleep (two 2-h blocks) and caloric requirements. Lower and upper limb CSE were determined with transcranial magnetic stimulation (TMS) stimulus-response curves. Self-reported resilience, physical activity, military-specific physical performance (TMT), and endocrine factors were compared in individuals with high (HIGH) and low CSE based on a median split of lower limb CSE at baseline. HIGH had greater physical activity and better TMT performance throughout SMOS. Both groups maintained physical performance despite substantial psychophysiological stress. Physical activity, resilience, and TMT performance were directly associated with lower limb CSE. Individual differences in physical activity coincide with lower (but not upper) limb CSE. Such use-dependent corticospinal excitability directly relates to resilience and physical performance during SMOS. Future studies may use noninvasive neuromodulation to clarify the interplay among CSE, physical activity, and resilience and improve physical and cognitive performance.NEW & NOTEWORTHY We demonstrate that individual differences in physical activity levels coincide with lower limb corticospinal excitability. Such use-dependent corticospinal excitability directly relates to resilience and physical performance during a 5-day simulation of military operational stress with caloric restriction, sleep restriction and disruption, and heavy physical and cognitive exertion.

Reliability of corticospinal excitability estimates for the vastus lateralis: Practical considerations for lower limb TMS task selection.

Transcranial magnetic stimulation (TMS) is increasingly used to examine lower extremity corticospinal excitability (CSE) in clinical and sports research. Because CSE is task-specific, there is growing emphasis on the use of ecological tasks. Nevertheless, the comparative reliability of CSE measurements during established (e.g. knee extensions; KE) and more recent ecological (e.g. squats; SQT) lower extremity tasks has received less attention. The aim of this study was to compare the test-retest reliability of CSE, force, and muscle activity (EMG) during isometric SQT and KE. 19 right-footed men (age: 25 ± 5 yrs) with similar fitness and body composition performed SQT (N = 7) or KE (N = 12) on two consecutive days. Force and EMG were recorded during maximum voluntary isometric contractions (MVC). Corticospinal excitability was determined in the dominant leg during light (15% MVC) contractions based on motor evoked potential (MEP) stimulus-response-curves (SRC). Test-retest reliability, absolute agreement, and consistency were determined for force, EMG, and SRC MEP maximum (MEPMAX) and rising phase midpoint (V50). As a secondary analysis, all outcomes were compared between groups with mixed-methods ANCOVAs (Task × Time, covariate: body-fat-percentage). Compared with SQT, KE displayed better test-retest reliability and agreement for MEPMAX whereas V50, force, and EMG were similarly reliable. Force (p = 0.01) and MEPMAX (p = 0.02) were also greater during KE despite a similar V50 (p = 0.11). Differences in test-retest reliability, absolute agreement, and between-group comparisons highlight the need to carefully select lower limb TMS assessment tasks and encourage future efforts to balance ecological validity with statistical sensitivity.

Characterizing off-target corticospinal responses to double-cone transcranial magnetic stimulation.

INTRODUCTION: The double-cone coil (D-CONE) is frequently used in transcranial magnetic stimulation (TMS) experiments that target the motor cortex (M1) lower-limb representation. Anecdotal evidence and modeling studies have shed light on the off-target effects of D-CONE TMS but the physiological extent remains undetermined. PURPOSE: To characterize the off-target effects of D-CONE TMS based on bilateral corticospinal responses in the legs and hands. METHODS: Thirty (N = 30) participants (9 women, age: 26 ± 5yrs) completed a stimulus-response curve procedure with D-CONE TMS applied to the dominant vastus lateralis (cVL) and motor-evoked potentials (MEPs) recorded in each active VL and resting first dorsal interosseous (FDI). As a positive control (CON), the dominant FDI was directly targeted with a figure-of-eight coil and MEPs were similarly recorded in each active FDI and resting VL. MEPMAX, V50 and MEP latencies were compared with repeated-measures ANOVAs or mixed-effects analysis and Bonferroni-corrected pairwise comparisons. RESULTS: Off-target responses were evident in all muscles, with similar MEPMAX in the target (cVL) and off-target (iVL) leg (p = 0.99) and cFDI compared with CON (p = 0.99). cFDI and CON MEPMAX were greater than iFDI (p < 0.01). A main effect of target (p < 0.001) indicated that latencies were shorter with CON but similar in all muscles with D-CONE. DISCUSSION: Concurrent MEP recordings in bilateral upper- and lower-extremity muscles confirm that lower-limb D-CONE TMS produces substantial distance-dependent off-target effects. In addition to monitoring corticospinal responses in off-target muscles to improve targeting accuracy in real-time, future studies may incorporate off-target information into statistical models post-hoc.

Active recovery shows favorable IGF-I and IGF binding protein responses following heavy resistance exercise compared to passive recovery.

IGF-I and IGFBPs have important physiological modulatory effects and this study sought to examine the influence of active vs. passive recovery following a heavy resistance exercise on IGF-I and IGF binding protein (IGFBP) recovery responses. It was hypothesized that increased IGF-I and decreased inhibitory IGFBPs during active recovery may be reflective of cascades promoting physiological recovery. 18 untrained men ((AR n = 7, PR n = 11), age: 26 ±â€¯4 years, height: 174 ±â€¯8 cm, body mass: 75 ±â€¯13 kg) performed either a protocol-specific 10 × 10 × 30% 1RM active (AR) or passive recovery (PR) session following a heavy resistance exercise session performed on a leg press device (10 × 10 1RM). Maximal isometric force production (MVC) and IGF- and IGFBPs were measured pre, post, 1-hr post, and next morning. A significantly greater relative response in IGF-I was observed in AR than in PR at post recovery and next morning (p < .01 and statistical trend, respectively) while absolute concentrations of IGFBP-1 at next morning were significantly higher in PR than AR (p < .05), and relative IGFBP-1 response from control to next morning in PR was significantly greater than in AR (p < .001). IGFBP-1 may be inhibitory to IGF-I biological action, thus the lower concentration of IGFBP-1 after AR may be considered favorable in terms of recovery due to its positive relationship with glucose metabolism and maintaining metabolic homeostasis. These results suggest that some of the benefits of an active recovery bout may be mediated by favorable IGF-I system responses (increased IGF-I and decreased IGFBP-1) in the hormonal milieu that may assist facilitating the cascade of physiological recovery processes following acute heavy resistance loading exercise.

Peripheral QCT sector analysis reveals early exercise-induced increases in tibial bone mineral density.

OBJECTIVES: The purpose of this controlled trial was to determine whether subtle changes in mineralization and geometry of the tibia were evident following short term exercise interventions. METHODS: Fifty-seven female volunteers (age 20.1±1.6) were randomized to one of four, 13-week training groups: sedentary control, resistance training, aerobic training, or combined aerobic-resistance. A pQCT image analysis software was developed and used to analyze images taken at sites 4%, 38% and 66% from the distal tibia at baseline and at completion of training. Parameters of bone mineral density, geometry and strength were determined for the entire scan cross-section and for each of six 60° polar sectors. Repeated-measures ANOVA and Fisher's LSD post hoc tests analyzed the effects of training over time. RESULTS: Trabecular density (TrDn) at the 4% site increased from 279.8±37.1 to 283.1±36.0 mg/cm(3) in the aerobic group, and from 285.1±24.6 to 287.5±22.9 mg/cm(3) in the combined group over the study period (P≤0.001). Regional sector analyses revealed that impact exercises resulted in localized changes to the medial aspect of the tibia. Small increases in total bone area were observed in the diaphysis (38% site) (P<0.05). CONCLUSIONS: Subtle, regional increases in trabecular density may be an early measurable manifestation of bone quality changes.

Female recruits sustaining stress fractures during military basic training demonstrate differential concentrations of circulating IGF-I system components: a preliminary study.

OBJECTIVE: Stress fracture injuries sustained during military basic combat training (BT) are a significant problem and occur at a higher rate in female recruits than male recruits. Insulin-like growth factor-I (IGF-I) is an easily measured biomarker that is involved in bone formation and positively correlated with bone mineral density, especially in women. This study examined the response of the IGF-I system between female soldiers that sustained a stress fracture (SFX, n=13) during BT and female soldiers who did not (NSFX, n=49). DESIGN: Female soldiers (n=62, 18.8 ± 0.6 yr) from 2 companies of a gender-integrated combat battalion in the Israeli Defense Forces participated in this study. Height, weight and blood draws were taken upon entry to BT (preBT) and after a four-month BT program (postBT). Stress fractures were diagnosed by bone scan. Serum was analyzed for total IGF-I, free IGF-I, IGF binding proteins (IGFBP)1-6, BAP, calcium, CTx, IL1ß, IL6, PINP, PTH, TNFα, TRAP, and 25(OH)D. Statistical differences between SFX and NSFX groups and time points were assessed by RM ANOVA with Fisher post-hoc (p≤0.05). RESULTS: The SFX group was significantly taller and had lower BMI than NSFX (p≤0.05). Serum concentrations of total IGF-I, bioavailable IGF-I, other bone biomarkers, and cytokines were not significantly different between SFX and NSFX preBT. Serum IGFBP-2 and IGFBP-5 were significantly higher in the SFX compared to the NSFX preBT (p≤0.05). In both groups, total IGF-I increased pre to postBT (p≤0.05). Additionally, a significant difference was observed in the bioavailable IGF-I response pre to postBT for both groups. The SFX group demonstrated a significant decrease in bioavailable IGF-I pre to postBT (preBT: 0.58 ± 0.58 ng/mL; postBT 0.39 ± 0.48; p≤0.05) whereas the NSFX group demonstrated a significant increase in bioavailable IGF-I pre to postBT (preBT: 0.53 ± 0.37 ng/mL; postBT: 0.63 ± 0.45; p≤0.05). CONCLUSIONS: Our study demonstrated that serum IGF-I changes during basic training and that women sustaining stress fractures during BT significantly decreased bioavailable IGF-I, whereas their uninjured counter parts increased bioavailable IGF-I. These results suggest that stress fracture susceptibility may be related to differential IGF-I system concentrations and response to physical training.

A novel, noninvasive transdermal fluid sampling methodology: IGF-I measurement following exercise.

This study tested the hypothesis that transdermal fluid (TDF) provides a more sensitive and accurate measure of exercise-induced increases in insulin-like growth factor-I (IGF-I) than serum, and that these increases are detectable proximal, but not distal, to the exercising muscle. A novel, noninvasive methodology was used to collect TDF, followed by sampling of total IGF-I (tIGF-I) and free IGF-I (fIGF-I) in TDF and serum following an acute bout of exercise. Experiment 1: eight men (23 ± 3 yrs, 79 ± 7 kg) underwent two conditions (resting and 60 min of cycling exercise at 60% Vo(2)(peak)) in which serum and forearm TDF were collected for comparison. There were no significant changes in tIGF-I or fIGF-I in TDF obtained from the forearm or from serum following exercise (P > 0.05); however, the proportion of fIGF-I to tIGF-I in TDF was approximately fourfold greater than that of serum (P ≤ 0.05). These data suggest that changes in TDF IGF-I are not evident when TDF is sampled distal from the working tissue. To determine whether exercise-induced increases in local IGF-I could be detected when TDF was sampled directly over the active muscle group, we performed a second experiment. Experiment 2: fourteen subjects (22 ± 4 yr, 68 ± 11 kg) underwent an acute plyometric exercise condition consisting of 10 sets of 10 plyometric jumps with 2-min rest between sets. We observed a significant increase in TDF tIGF-I following exercise (P ≤ 0.05) but no change in serum tIGF-I (P > 0.05). Overall, these data suggest that TDF may provide a noninvasive means of monitoring acute exercise-induced changes in local IGF-I when sampled in proximity to exercising muscles. Moreover, our finding that the proportion of free to tIGF-I was greater in TDF than in serum suggests that changes in local IGF-I may be captured more readily using this system.

Three-month bilateral hopping intervention is ineffective in initiating bone biomarker response in healthy elderly men.

In animal studies, bone adaptation has been initiated successfully without the transient force spike associated with high impact exercises. Consequently, a 12-week bilateral hopping on the balls of the feet intervention was conducted. 25 elderly men (age 72(SD4) years, height 171(6) cm, weight 75(9) kg) were randomly assigned into exercise and control groups. Ten subjects in each group completed the study. Carboxyterminal propeptide of type I collagen (CICP), bone-specific alkaline phosphatase (bALP) and carboxyterminal telopeptide of type I collagen (CTx) were measured from venous blood samples at baseline, at 2 weeks and at the end of the intervention. Maximal ground reaction force (GRF), osteogenic index (OI) and jump height (JH) were determined from bilateral hopping test and balance was assessed with velocity of center of pressure (COP(velocity)) while standing on the preferred leg with eyes open. The intervention consisted of 5-7 sets of 10 s timed bilateral hopping exercise at 75-90% intensity three times/week. There was no significant group × time interaction for GRF, OI and JH (P = 0.065). GRF (11% change from baseline vs. 4%), OI (15 vs. 6%) and COP(velocity) (-10 vs. -1%) were not influenced by the intervention (P > 0.170), while the control group improved JH (P = 0.031) (2 vs. 18%). For the biomarkers, no effect was observed in MANOVA (P = 0.536) or in univariate analyses (P = 0.082 to P = 0.820) (CICP -2 vs. -3%, CTx 8 vs. -12%, bALP 0 vs. -3.7%). Allowing transient impact force spikes may be necessary to initiate a bone response in elderly men as the intervention was ineffective.

Relationship between growth hormone in vivo bioactivity, the insulin-like growth factor-I system and bone mineral density in young, physically fit men and women.

CONTEXT: Bone mineral density (BMD) is influenced by growth factors, such as growth hormone (GH) and insulin-like growth factor-I (IGF-I). The in vivo bioassay for GH (bioGH) provides a more physiologically relevant measurement than an in vitro immunoassay, since bioGH is quantified on a biological outcome. OBJECTIVE: To determine if bioGH and components of the IGF-I system were associated with BMD in age-matched men (M; n=41, 19.1+/-0.2 year, 70+/-3 kg, 163+/-25 cm) and women (W; n=39, 18.6+/-0.3 year, 66+/-3 kg, 141+/-15 cm). DESIGN: Blood was analyzed for growth-related hormones [bioGH, immunoreactive growth hormone (iGH), IGF-I and associated binding proteins], and BMD was measured by pDXA, pQCT, and central DXA (spine, hip). For the bioGH assay, hypophysectomizied female Sprague-Dawley rats were injected with a s.c. bolus of either a GH standard or unknown (each subject's plasma) in four daily injections. The tibia was then examined for epiphyseal growth plate width from which bioGH concentrations were extrapolated. RESULTS: M had greater (P<0.05) calcaneal BMD when measured by pDXA (M: 1.27+/-0.02; W: 1.14+/-0.02 g/cm2), while pQCT-assessed BMD at the tibia was not different (M: 777+/-16; W: 799+/-16 g/cm2). bioGH was similar between M (5388+/-800 microg/L) and W (4282+/-643 microg/L) and was not correlated with BMD. The only BMD-related biomarkers in women were acid-labile subunit (ALS; r=0.40) and IGFBP-3 (r=0.42) with DXA-measured spine and femoral neck BMD, and ALS (r=0.47) with pQCT-assessed tibial BMD and cortical thickness, respectively. CONCLUSION: Although bioGH was not associated with BMD, IGF-I and associated binding proteins (IGFBP-3 and ALS) emerged as correlates in W only.

Effects of intensified military field training on jumping performance.

A sensitive, reliable, field-expedient test may be valuable for monitoring interventions during periods of anticipated physical performance decline. The purpose of this study was to determine the capabilities of unloaded jumping tests for detecting decrements in physical performance following eight days of military sustained operations. Twenty-nine U. S. Marines (24 +/- 1 y; 180 +/- 6 cm; 82.5 +/- 8.2 kg) performed 1, 5 and 30 repetition(s) of unloaded countermovement jumps (UJ) before and after eight days of sustained operations (SUSOPS). Jump performance data was collected simultaneously using a switch mat (SM) and a linear position transducer (LPT). Jump height (m) and power (W) were highest using 1 UJ and declined 4.9 and 8.9%, respectively after SUSOPS. Jump power (JP) declined progressively over 30 UJ (20%). Five UJ offered no advantages over 1 UJ and was inadequate to examine changes in muscle fatigability (pre: 1294 +/- 138 W; post: 1250 +/- 165 W). The SM and a LPT were in agreement and had a high correlation (r = 0.92). One UJ was a sensitive, easy to implement test for monitoring the collective impact of high physical, nutritional, cognitive, and environmental stress on an individuals' physical performance before and after 8 days of SUSOPS, suggesting decrements in physical performance associated with overreaching can be detected by simply administered field-expedient jumping tests.

Influence of muscle strength and total work on exercise-induced plasma growth hormone isoforms in women.

The purpose of this investigation was to determine the influence of physical strength and the ability to do more total work on human growth hormone (GH) variants to a heavy resistance exercise protocol in untrained women. From a distribution of 100 healthy, untrained women, the strongest 10 women (S) and the weakest 10 women (W) were compared for GH responses pre- and post an acute heavy resistance exercise test (AHRET, 6 sets of 10 RM squats, 2 minutes rest between sets). Blood samples were obtained pre-exercise and immediately post-exercise and subsequently analysed in total as well as fractionated by Sephacryl S-100R column chromatography into three molecular weight size classes: fraction A: > 60 kD, fraction B: 30-60 kD, fraction C: < 30 kD. For each total sample as well as each fraction, immunoreactive GH was measured via the Nichols IRMA, while bioactive GH was measured via the hypox rat tibial line bioassay and Diagnostic Systems Laboratory's immunofunctional GH ELISA. No exercise-induced changes or differences between groups were observed in the tibial line bioassay. However, the S group displayed a significantly higher pre-exercise resting value in the total fraction than the W group. Conversely, the W group exhibited a significantly higher pre-exercise value in the smaller molecular weight fraction C. With regards to the immunofunctional and immunoreactive assays, the total fraction, fraction A, and fraction B demonstrated significant (P < or = 0.05) exercise-induced increases in both the S and W group despite no group differences. For the Nichols and immunofunctional assays significant exercise-induced changes were observed in the smaller molecular weight C fraction in the W group but not the S group. However, the S group displayed a significantly higher pre-exercise value in fraction C relative to the W group. These data demonstrate for the first time that differences exist in the GH molecular weight variants between strong and weak untrained women, with the lower molecular weight variants seemingly less responsive to greater amounts of exercise in stronger women, thus suggesting differential regulation of GH molecular weight variants during resistance exercise due to pre-existing physical parameters.

Strength, workload, anaerobic intensity and the immune response to resistance exercise in women.

AIM: The mechanism linking exercise intensity to the magnitude of the immune response is not completely understood. The purpose of this investigation was to determine whether the immune response to resistance exercise was associated with (1) changes in workload or (2) anaerobic exercise intensity. METHODS: Previously untrained women underwent 6 months of resistance training for lower and upper body (TOTAL, n = 34) or for upper body alone (UPPER, n = 30). Lymphocyte subsets [T (CD3+), CD4+, CD8+, NK and B], functional markers (CD45RA+ and CD45RO+), and mitogen (phytohemagglutinin-M, concanavalin A and pokeweed mitogen) and superantigen (staphylococcus a. cowans)-stimulated proliferation were measured from blood samples collected pre- and post-exercise for a squat resistance exercise consisting of six sets of 10 repetitions at 75% of one repetition maximum. This protocol was performed before (T0) and after 3 (T3) and 6 months (T6) of training. RESULTS: Lymphocyte recruitment to the circulation and proliferation following resistance exercise did not differ between training groups at any time, although the TOTAL group performed at a higher workload as training progressed. With respect to anaerobic intensity, exercise-induced increases in NK, CD4+, CD8+ and B lymphocyte concentrations were 42 (P = 0.07), 76 (P < 0.05), 72 (P < 0.05) and 242% (P < 0.01) greater in women in the highest compared with the lowest post-exercise lactate quartiles. Lymphocyte proliferation did not differ between lactate quartiles. CONCLUSIONS: Anaerobic intensity, rather than increased strength and workload, is associated with the number of lymphocytes recruited to the circulation, but not T and B cell proliferation responses.

Comparison of creatine ingestion and resistance training on energy expenditure and limb blood flow.

This study determined the effects of 28 days of oral creatine ingestion (days 1 to 5 = 20g/d; [5 g 4 times daily]: days 6 to 28 = 10 g/d; [5 g twice daily]) alone and with resistance training (5 hours/week) on resting metabolic rate (RMR), body composition, muscular strength (1RM), and limb blood flow (LBF). Using a double-blind, placebo-controlled design, 30 healthy male volunteers (21 +/- 3 years; 18 to 30 years) were randomly assigned to 1 of 3 groups; pure creatine monohydrate alone (Cr; n = 10), creatine plus resistance training (Cr-RT; n = 10), or placebo plus resistance training (P-RT; n = 10). Body composition (DEXA, Lunar DPX-IQ), body mass, bench, and leg press 1RM (isotonic), RMR (indirect calorimetry; ventilated hood), and forearm and calf LBF (venous occlusive plethysmography) were obtained on all 30 subjects on 3 occasions beginning at approximately 6:00 AM following an overnight fast and 24 hours removed from the last training session; baseline (day 0), and 7 days and 29 days following the interventions. No differences existed among groups at baseline for any of the variables measured. Following the 28-day interventions, body mass (Cr, 73.9 +/- 11.5 v 75.6 +/- 12.5 kg; Cr-RT, 78.8 +/- 6.7 v 80.8 +/- 6.8 kg; P <.01) and total body water (Cr, 40.4 +/- 6.8 v 42.6 +/- 7.2 L, 5.5%; Cr-RT, 40.6 +/- 2.4 v 42.3 +/- 2.2 L, 4.3%; P <.01) increased significantly in Cr and Cr-RT, but remained unchanged in P-RT, whereas, fat-free mass (FFM) increased significantly in Cr-RT (63 +/- 2.8 v 64.7 +/- 3.6 kg; P <.01) and showed a tendency to increase in Cr (58.1 +/- 8.1 v 59 +/- 8.8 kg; P =.07). Following the 28-day period, all groups significantly increased (P <.01) bench (Cr, 77.3 +/- 4 v 83.2 +/- 3.6 kg; Cr-RT, 76.8 +/- 4.5 v 90.5 +/- 4.5 kg; P-RT, 76.0 +/- 3.4 v 85.5 +/- 3.2 kg), and leg press (Cr, 205.5 +/- 14.5 v 238.6 +/- 13.2 kg; Cr-RT, 167.7 +/- 13.2 v 238.6 +/- 17.3 kg; P-RT, 200.5 +/- 9.5 v 255 +/- 13.2 kg) 1RM muscular strength. However, Cr-RT improved significantly more (P <.05) on the leg press 1RM than Cr and P-RT and the bench press 1RM than Cr (P <.01). Calf (30%) and forearm (38%) LBF increased significantly (P <.05) in the Cr-RT, but remained unchanged in the Cr and P-RT groups following the supplementation period. RMR expressed on an absolute basis was increased in the Cr (1,860.1 +/- 164.9 v 1,907 +/- 173.4 kcal/d, 2.5%; P <.05) and Cr-RT (1,971.4 +/- 171.8 v 2,085.7 +/- 183.6 kcal/d, 5%; P <.05), but remained unchanged from baseline in P-RT. Total cholesterol decreased significantly in Cr-RT (-9.9%; 172 +/- 27 v 155 +/- 26 mg/dL; P <.01) compared with Cr (174 +/- 46 v 178 +/- 43 mg/dL) and P-RT (162 +/- 32 v 161 +/- 36 mg/dL) following the 28-day intervention. These findings suggest that the addition of creatine supplementation to resistance training significantly increases total and fat-free body mass, muscular strength, peripheral blood flow, and resting energy expenditure and improves blood cholesterol.

Lymphocyte proliferation in response to acute heavy resistance exercise in women: influence of muscle strength and total work.

Little is understood about the immune responses to heavy resistance exercise. The purpose of this investigation was to determine the influence of physical strength and the ability to do more total work on lymphocyte proliferation after an acute bout of heavy resistance exercise. A group of 50 healthy but nonstrength trained women were recruited for the study and tested for their one repetition maximum (i.e. 1 RM or maximal mass lifted once). From the normal distribution of strength the top and bottom 8 women [mean age 22.5 (SD 3.1) years] were asked to volunteer to define our two groups (i.e. high strength and low strength). The two groups were significantly different (P < 0.05) in 1 RM squat strength [low strength 39.9 (SD 4.6) kg, 0.65 (SD 0.08) kg.kg body mass-1 and high strength 72.2 (SD 10.7) kg, 1.1 (SD 0.12) kg.kg body mass-1] but were not significantly different in body mass, age, activity levels, and menstrual status (all in same phase). Each performed a resistance exercise protocol consisting of six sets of 10 RM squats with 2 min rest between the sets. The 10 RM loads and total work were significantly greater in the high strength group than in the low strength group. Blood samples were obtained pre-exercise and immediately post-exercise for test for lactate (significant increase with exercise) and cortisol (no changes) concentrations with no differences noted between groups. Immunological assays on the blood samples determined the incorporation of tritiated thymidine by lymphocytes in responses to concanavalin A (ConA), phytohemagglutinin (PHA), and pokeweed mitogen (PWM). Following the squat exercise, there was a significant decrease in lymphocyte responsiveness to PWM in the high strength but not in the low strength group for both total proliferation and proliferation adjusted per B or T cell. On the other hand, lymphocytes from the low strength group proliferated to a significantly greater extent (adjusted per T cell) in response to ConA and PHA. These data indicate that the heavy resistance exercise protocol reduced the lymphocyte proliferative responses only in the stronger group of subjects. This effect may have been due to the high absolute total work and the greater exercise stress created by the resistance exercise protocol in the high strength group. Therefore, individuals performing at the same relative exercise intensity (i.e. 10 RM) in a resistance exercise protocol may have different immune responses stemming from differences in absolute total work performance.

Characteristics of circulating growth hormone in women after acute heavy resistance exercise.

The effects of exercise on the molecular nature of secreted human growth hormone (GH) or its biological activity are not well understood. Plasma from women (average age 23.6 yr, n = 35), drawn before and after an acute heavy resistance exercise test, was fractionated by size exclusion chromatography into three size classes, namely, > 60 kDa (fraction A), 30-60 kDa (fraction B), and < 30 kDa (fraction C), before GH assay. Concentrations of GH in these fractions, as well as in unfractioned plasma, were measured by the Nichols immunoradiometric assay, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) polyclonal competitive RIA, Diagnostic Systems Laboratory's immunofunctional assay (measures dimerization-capable species), and the rat tibial bioassay. Significantly increased circulating GH concentrations of two- to fourfold were observed when immunoassays in unfractionated plasma samples were used, but they showed no significant change with use of the rat tibial bioassay. Significant exercise-induced increases in GH were found in fractions B and C but not in fraction A. Because chemical reduction of the samples before GH immunoassay significantly increased GH concentrations in fractions B and C (Nichols and NIDDK kits) after exercise, it is concluded that exercise may specifically increase release of disulfide-linked hormone molecules and/or fragments. Finally, because most of the GH released after exercise was able to dimerize the GH receptor in vitro, it is also concluded that these forms have the two intact binding sites required to initiate signal transduction in target cells.