National Institutes of Health

University of Massachusetts Amherst

Edith Cowan University

Queensland University of Technology

Karolinska Institutet

Pennington Biomedical Research Center

Appalachian State University

Arizona State University

Beaumont Health System

Gramercy Research Group

Columbia University

Stockholm University

Uppsala University

Norwegian School of Sport Sciences (NIH)

The Ohio State University

University of South Carolina

San Diego State University

University of Rhode Island

Teesside University

William & Mary

University of Tennessee

University of Minnesota Twin Cities

Ball State University

University of Wisconsin - Milwaukee

The College of New Jersey

Penn State Hershey Medical Center and Penn State College of Medicine

This journal's original articles report on new educational developments as well as sound physical fitness practices and the treatment of sports injuries. The journal helps readers enhance their basic understanding about the role of physical activity in human health and function.

Medicine and Science in Sports and Exercise

Response.

RESPONSE.

Purpose: 
Resistance training combined with appropriate dietary intake can promote a concomitant increase in skeletal muscle mass (SMM) and reduction in fat mass, a condition termed body recomposition. This study's primary purpose was to explore the effects of protein ingestion on body recomposition following 24 weeks of resistance training (RT) in older women.

Methods: 
Data from 130 untrained older women (68.7 ± 5.6 years, 66.5 ± 11.5 kg, 155.5 ± 6.0 cm, and 27.4 ± 4.0 kg.m-2) across six studies were retrospectively analyzed. The participants were divided into tertiles according to their customary protein intake (g/kg/d): lower (LP, n = 45), moderate (MP, n = 42), and higher (HP, n = 43) protein intake. Participants performed a whole-body RT program carried out over 24 weeks (eight exercises, three sets, 8-15 repetitions, three sessions a week). SMM and fat mass were determined by dual-energy X-ray absorptiometry.

Results: 
All groups increased SMM from baseline (P < 0.05), with the HP and MP groups showing greater increases than the LP group (LP = 2.3%, MP = 5.4%, and HP = 5.1%; P < 0.05). Reductions in fat mass were similar for all three groups (LP = 1.7%, MP = 3.7%, and HP = 3.1%; P > 0.05). The composite Z-score of the percentage changes from pre- to post-training indicated greater positive body recomposition values for HP and MP compared to LP (P < 0.05).

Conclusions: 
Results suggest that protein intake is a moderating variable for body recomposition in older women undergoing RT, with a low protein intake having a less favorable effect on body recomposition.

Moderate and Higher Protein Intakes Promote Superior Body Recomposition in Older Women Performing Resistance Training

This consensus statement is an update of the 2010 American College of Sports Medicine position stand on exercise and type 2 diabetes. Since then, a substantial amount of research on select topics in exercise in individuals of various ages with type 2 diabetes has been published while diabetes prevalence has continued to expand worldwide. This consensus statement provides a brief summary of the current evidence and extends and updates the prior recommendations. The document has been expanded to include physical activity, a broader, more comprehensive definition of human movement than planned exercise, and reducing sedentary time. Various types of physical activity enhance health and glycemic management in people with type 2 diabetes, including flexibility and balance exercise, and the importance of each recommended type or mode are discussed. In general, the 2018 Physical Activity Guidelines for Americans apply to all individuals with type 2 diabetes, with a few exceptions and modifications. People with type 2 diabetes should engage in physical activity regularly and be encouraged to reduce sedentary time and break up sitting time with frequent activity breaks. Any activities undertaken with acute and chronic health complications related to diabetes may require accommodations to ensure safe and effective participation. Other topics addressed are exercise timing to maximize its glucose-lowering effects and barriers to and inequities in physical activity adoption and maintenance.

Exercise/Physical Activity in Individuals with Type 2 Diabetes: A Consensus Statement from the American College of Sports Medicine

Polarized Training Is Not Optimal for Endurance Athletes

Purpose: 
The aim of our study was to compare maximal force, force steadiness, and discharge characteristics of motor units in tibialis anterior during contractions with the dorsiflexors of the dominant and non-dominant legs at low-to-moderate target forces and three ankle angles.

Methods: 
Twenty young adults performed maximal and submaximal isometric contractions (5, 10, 20, 40, and 60% of maximal voluntary contraction, MVC) with the dorsiflexors of the dominant and non-dominant legs at three ankle angles (75ο = short length, 90ο = intermediate length, 105o = long length). High-density electromyographic (EMG) signals from the tibialis anterior muscle of each leg were recorded.

Results: 
Maximal force (average dominant: 182.9 ± 64.5 N; non-dominant: 179.0 ± 58.8 N) and the fluctuations in force, quantified as absolute (standard deviation) and normalized amplitudes (coefficient of variation, CoV), were similar between the two legs across the three ankle angles (average CoV for dominant: 1.5 ± 1.0%; non-dominant: 1.7 ± 1.3 %). The CoV for force for both legs decreased from 5 to 20% MVC force and then it plateaued at 40 and 60% MVC force. EMG amplitude, mean discharge rate of motor units, discharge variability (interspike interval), and the variability in neural drive (filtered cumulative spike train) were similar between the two legs across the submaximal contractions.

Conclusions: 
MVC force and force steadiness were similar across ankle angles and target forces between the dominant and non-dominant legs. The attributes that underlie the self-reported identification of a dominant leg were not associated with the force capacity or the control of force for the dorsiflexor muscles, at least during isometric contractions.

Leg Dominance Does Not Influence Maximal Force, Force Steadiness, or Motor Unit Discharge Characteristics

Purpose: 
To investigate the effect of intensity and duration of continuous and interval exercise training on capillarization in skeletal muscle of healthy adults.

Methods: 
PubMed and Web of Science were searched from inception to June 2021. Eligibility criteria for studies were: endurance exercise training >2 wks in healthy adults, and capillary to fiber ratio (C:F) and/or capillary density (CD) reported. Meta-analyses were performed and subsequent subgroup analyses were conducted by the characteristics of participants and training scheme.

Results: 
57 trials from 38 studies were included (10/90%, athletic/sedentary). C:F was measured in 391 subjects from 47 trials while CD was measured in 428 subjects from 50 trials. Exercise training increased C:F (Mean difference (MD) 0.33 [0.30-0.37; 95% CI]) with low heterogeneity (I2 = 45.08 %) and CD (MD 49.8 [36.9-62.6] Cap/mm2) with moderate heterogeneity (I2 = 68.82%). Compared to low intensity training (LOW, <50% of VO2max), 21% higher relative change in C:F ratio was observed after continuous moderate intensity training (CON, 50-80%VO2max) and 54% higher change after interval training with high intensity (INT, 80-100% of VO2max) in sedentary subjects. The magnitude of capillary growth was not dependent on training intervention duration. In already trained subjects, no additional increase in capillarization was observed with various types of training.

Conclusions: 
In sedentary subjects, CON and INT leads to increases in capillarization, whereas LOW has less effect. Within the timeframe studied, no effect on capillarization was established regarding training duration in sedentary subjects. The meta-analysis highlights the need for further studies in athlete groups to discern if increased capillarization can be obtained, and if so, which combination is optimal (time vs intensity).

Effects of Exercise Training Intensity and Duration on Skeletal Muscle Capillarization in Healthy Subjects: A Meta-analysis

Polarized Training Is Not Optimal for Endurance Athletes: Response to Foster and Colleagues

Comparing Workload Between Halves And Its Association To Anthropometry And Cardiorespiratory Performance In Female Collegiate Soccer Players

Introduction: 
A paucity of research exists examining the importance of muscle morphological and functional characteristics for elite female sprint performance.

Purpose: 
This study aimed to compare lower body muscle volumes and vertical jumping power between elite vs. sub-elite female sprinters; and assess the relationships of these characteristics with sprint race and acceleration performance.

Methods: 
Five elite (100 m seasons best [SBE100]: 11.16 ± 0.06 s) and 17 sub-elite (SBE100 11.84 ± 0.42 s) female sprinters underwent: 3 T magnetic resonance imaging to determine the volume of 23 individual leg muscles/compartments and five functional muscle groups; countermovement jump (CMJ) and 30 m acceleration tests.

Results: 
Total absolute lower body muscle volume was higher in elite vs. sub-elite sprinters (+15%). Elite females exhibited greater muscle volume of the hip flexors (absolute +28%, relative [to body mass] +19%), hip extensors (absolute +22%, relative +14%), and knee extensors (absolute +21%), demonstrating pronounced anatomically specific muscularity, with relative hip flexor volume alone explaining 48% of sprint performance variability. The relative volume of five individual muscles (sartorius, gluteus maximus, adductor magnus, vastus lateralis, illiopsoas) were both distinct between groups (elite > sub-elite) and related to SBE100 (r = 0.553-0.639), with the combination of the sartorius (41%) and the adductor magnus (17%) explaining 58% of the variance in SBE100. Elite female sprinters demonstrated greater absolute CMJ power vs. sub-elite, and absolute and relative power were related to both SBE100 (r = -0.520 to -0.741) and acceleration performance (r = 0.569 to 0.808).

Conclusions: 
This investigation illustrates the distinctive, anatomically specific muscle volume distribution that facilitates elite sprint running in females, and emphasises the importance of hip flexor and extensor relative muscle volume.

The Muscle Morphology of Elite Female Sprint Running

Purpose: 
This study aimed to compare and rank gluteal muscle forces in eight hip-focused exercises performed with and without external resistance and describe the underlying fiber lengths, velocities, and muscle activations.

Methods: 
Motion capture, ground reaction forces, and electromyography (EMG) were used as input to an EMG-informed neuromusculoskeletal model to estimate gluteus maximus, medius, and minimus muscle forces. Participants were 14 female footballers (18-32 yr old) with at least 3 months of lower limb strength training experience. Each participant performed eight hip-focused exercises (single-leg squat, split squat, single-leg Romanian deadlift [RDL], single-leg hip thrust, banded side step, hip hike, side plank, and side-lying leg raise) with and without 12 repetition maximum (RM) resistance. For each muscle, exercises were ranked by peak muscle force, and k-means clustering separated exercises into four tiers.

Results: 
The tier 1 exercises for gluteus maximus were loaded split squat (95% confidence interval [CI] = 495-688 N), loaded single-leg RDL (95% CI = 500-655 N), and loaded single-leg hip thrust (95% CI = 505-640 N). The tier 1 exercises for gluteus medius were body weight side plank (95% CI = 338-483 N), loaded single-leg squat (95% CI = 278-422 N), and loaded single-leg RDL (95% CI = 283-405 N). The tier 1 exercises for gluteus minimus were loaded single-leg RDL (95% CI = 267-389 N) and body weight side plank (95% CI = 272-382 N). Peak gluteal muscle forces increased by 28-150 N when exercises were performed with 12RM external resistance compared with body weight only. Peak muscle force coincided with maximum fiber length for most exercises.

Conclusions: 
Gluteal muscle forces were exercise specific, and peak muscle forces increased by varying amounts when adding a 12RM external resistance. These findings may inform exercise selection by facilitating the targeting of individual gluteal muscles and optimization of mechanical loads to match performance, injury prevention, or rehabilitation training goals.

Gluteal Muscle Forces during Hip-Focused Injury Prevention and Rehabilitation Exercises

Aim: 
This study investigated the development of power profiles and performance-related measures from the junior level (<19 years) via U23 (19-23 years) to senior level (>23 years) in 19 female and 100 male Norwegian national team cyclists.

Methods: 
A total of 285 tests were performed in a 3-day laboratory-standardized testing regime. The tests included power profiles with shorter duration (6-60 s) and longer durations (12-30 min) together with performance-related measures: Critical power (CP), work capacity above CP (W'), power output at 4 and 2 mmol·L-1 [BLa-] (L4 and L2), maximal aerobic power (Wmax), and maximal oxygen uptake (VO2max), gross efficiency (GE), and pedalling efficiency.

Results: 
Females and males evolve similarly when maturing from junior via U23 to senior categories (all p > 0.07), except for VO2max which increased in females (but not males) from junior to senior level (534 ± 436 ml·min-1, p = 0.013). In general, only performances of longer durations improved with age (12-min and 30-min, p = 0.028, and p = 0.042, respectively). Performance-related measures like Wmax, VO2max, CP, L4, L2, and pedalling efficiency in the fresh state improved with age (all p ≤ 0.025). Importantly, performance in the semi-fatigued state during a 5-min maximal test, was also improved with age (p = 0.045) despite a higher external energy expenditure prior to the test (p = 0.026).

Conclusions: 
Junior cyclists show highly developed sprint-abilities, and the primary improvements of absolute power outputs and performance-related measures are seen for durations >60 s when maturing to U23 and senior categories. However, the durability, i.e., the capacity to maintain performance in a semi-fatigued state is improved with age.

Development of Cycling Performance-Variables and Durability in Female and Male National Team Cyclists: From Junior to Senior

Purpose: 
We aimed to test the extended capabilities of the SRS protocol by validating its capacity to predict the power outputs for targeted metabolic rates (V̇O2) and time-to-task failure (Tlim) within the heavy- and severe-intensity domain, respectively.

Methods: 
Fourteen young individuals completed i) a SRS protocol from which the power outputs at GET and RCP (RCPCORR), and the work accruable above RCPCORR, defined as W´RAMP, were derived; ii) one heavy-intensity bout at a power output predicted to elicit a targeted V̇O2 equidistant from GET and RCP; iii) four severe-intensity trials at power outputs predicted to elicit targeted Tlim at minutes 2.5, 5, 10, and 13. These severe-intensity trials were also used to compute the constant load-derived critical power (CP) and W´ (W´CONSTANT).

Results: 
Targeted (2.41 ± 0.52 L·min-1) and measured (2.43 ± 0.52 L·min-1) V̇O2 at the identified heavy-intensity power output (162 ± 43 W) were not different (P = 0.71) and substantially concordant (CCC = 0.95). Likewise, targeted and measured Tlim for the four identified severe-intensity power outputs were not different (P > 0.05) and the aggregated coefficient of variation was 10.7 ± 8.9 %. The derived power outputs at RCPCORR (192 ± 53 W) and CP (193 ± 53 W) were not different (P = 0.65) and highly concordant (CCC = 0.99). There were also no differences between W´RAMP and W´CONSTANT (P = 0.51).

Conclusions: 
The SRS protocol can accurately predict power outputs to elicit discrete metabolic rates and exercise durations, thus providing, with time efficiency, a high precision for the control of the metabolic stimulus during exercise.

A Single Test Protocol to Establish the Full Spectrum of Exercise Intensity Prescription

Purpose: 
To compare the effects of free-weight and machine-based resistance training on strength, hypertrophy, and joint discomfort.

Methods: 
Thirty-eight resistance-trained men participated in an 8-week resistance program allocated into free-weight (n = 19) or machine-based (n = 19) groups. Training variables were identical for both modalities, so they only differed in the use of barbells or machines to execute the full squat, bench press, prone bench pull, and shoulder press exercises. The velocity-based method was implemented to accurately adjust the intensity throughout the program. Strength changes were evaluated using 8 velocity-monitored loading tests (4 exercises x 2 modalities) and included the relative one-repetition maximum (1RMRel), as well as the mean propulsive velocity against low (MPVLow) and high (MPVHigh) loads. Ultrasound-derived cross-sectional area (CSA) of quadriceps (proximal and distal regions), pectoralis major, and rectus abdominis was measured to examine hypertrophy. Complementarily, WOMAC and DASH questionnaires were administrated to assess changes in lower- and upper-limb joint discomfort. Outcomes were compared using ANCOVA and percentage of change (∆) statistics.

Results: 
Each group significantly (p < 0.001) increased 1RMRel, MPVLow, and MPVHigh for both modalities tested, but especially in the one they trained. When considering together the 8 exercises tested, strength changes for both modalities were similar (∆ differences ≤1.8%, p ≥ 0.216). Likewise, the CSA of all the muscles evaluated was significantly increased by both modalities, with no significant differences between them (∆ difference ≤ 2.0%, p ≥ 0.208). No between-group differences (p ≥ 0.144) were found for changes in stiffness, pain, and functional disability levels, which were reduced by both modalities.

Conclusions: 
Free-weight and machine-based modalities are similarly effective to promote strength and hypertrophy without increasing joint discomfort.

Free-Weight and Machine-Based Training Are Equally Effective on Strength and Hypertrophy: Challenging a Traditional Myth

Biological sex is a primary determinant of athletic performance because of fundamental sex differences in anatomy and physiology dictated by sex chromosomes and sex hormones. Adult men are typically stronger, more powerful, and faster than women of similar age and training status. Thus, for athletic events and sports relying on endurance, muscle strength, speed, and power, males typically outperform females by 10%–30% depending on the requirements of the event. These sex differences in performance emerge with the onset of puberty and coincide with the increase in endogenous sex steroid hormones, in particular testosterone in males, which increases 30-fold by adulthood, but remains low in females. The primary goal of this consensus statement is to provide the latest scientific knowledge and mechanisms for the sex differences in athletic performance. This review highlights the differences in anatomy and physiology between males and females that are primary determinants of the sex differences in athletic performance and in response to exercise training, and the role of sex steroid hormones (particularly testosterone and estradiol). We also identify historical and nonphysiological factors that influence the sex differences in performance. Finally, we identify gaps in the knowledge of sex differences in athletic performance and the underlying mechanisms, providing substantial opportunities for high-impact studies. A major step toward closing the knowledge gap is to include more and equitable numbers of women to that of men in mechanistic studies that determine any of the sex differences in response to an acute bout of exercise, exercise training, and athletic performance.

The Biological Basis of Sex Differences in Athletic Performance: Consensus Statement for the American College of Sports Medicine

Purpose
This study investigated the effect of progressively adding sets for the lower- limb every two weeks versus performing a constant set volume in resistance-trained males.

Methods
Thirty-one resistance-trained males (age 24.4 ± 2.9 years; height 175.5 ± 6.5 cm; body mass 80.1 ± 9.4 kg; body fat 14.4 ± 3.1%; resistance training [RT] experience 5.1 ± 2.2 years; one repetition maximum (1-RM) barbell back squat:body mass ratio 1.7 ± 0.1 a.u.) were randomly allocated into a Constant Group (CG, n = 10), a four sets progression group (4SG, n = 10) or a six sets progression group (6SG, n = 11). After a 2-week washout period and another 2-week familiarization period, participants performed a lower-limb training program twice a week for 12 weeks. Maximum dynamic strength (1-RM) in the barbell back squat, vastus lateralis cross-sectional area (CSA), and the sum of lateral thigh muscle thickness (∑MT) at 30, 50 and 70% of the femur length were assessed at baseline and after the 12-week training program.

Results
Regarding 1-RM, multiple comparisons revealed that 6SG elicited higher muscle strength gains than 4SG (p = 0.002) and CG (p < 0.0001), and 4SG had greater improvements than CG (p = 0.023). CSA and ∑MT showed no between-group differences (p = 0.067 and p = 0.076, respectively). However, an inspection of 95% confidence intervals suggests a potential dose-response relationship, with results appearing to plateau in the higher volume conditions.

Conclusions
Our results suggest that progressively adding four or six sets per week every two weeks elicited greater lower-limb strength in resistance-trained individuals over a 12-week training period. While our findings indicate a possible small benefit for higher volume conditions regarding hypertrophic adaptations in this population, the limited certainty of our findings warrants caution.

Effects of Different Weekly Set Progressions on Muscular Adaptations in Trained Males: Is there a Dose-Response Effect?

Purpose
To evaluate patellar tendon loading profiles (loading index, based on loading peak, loading impulse, and loading rate) of rehabilitation exercises to develop clinical guidelines to incrementally increase the rate and magnitude of patellar tendon loading during rehabilitation.

Methods
Twenty healthy adults (10 females/10 males, 25.9 ± 5.7 years) performed 35 rehabilitation exercises, including different variations of squats, lunge, jumps, hops, landings, running, and sports specific tasks. Kinematic and kinetic data were collected and a patellar tendon loading index was determined for each exercise using a weighted sum of loading peak, loading rate, and cumulative loading impulse. Then, the exercises were ranked, according to the loading index, into tier 1 (loading index≤0.33), tier 2 (0.33 < loading index<0.66), and tier 3 (loading index≥0.66).

Results
The single-leg decline squat showed the highest loading index (0.747). Other tier 3 exercises included single-leg forward hop (0.666), single-leg countermovement jump (0.711), and running cut (0.725). The Spanish squat was categorized as a tier 2 exercise (0.563), as was running (0.612), double-leg countermovement jump (0.610), single-leg drop vertical jump (0.599), single-leg full squat (0.580), double-leg drop vertical jump (0.563), lunge (0.471), double-leg full squat (0.428), single-leg 60° squat (0.411), and the Bulgarian squat (0.406). Tier 1 exercises included 20 cm step up (0.187), 20 cm step down (0.288), 30 cm step up (0.321), and double-leg 60° squat (0.224).

Conclusions
Three patellar tendon loading tiers were established based on a combination of loading peak, loading impulse, and loading rate. Clinicians may use these loading tiers as a guide to progressively increase patellar tendon loading during the rehabilitation of patients with patellar tendon disorders and after anterior cruciate ligament reconstruction using the bone patellar tendon bone graft.

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