Throwing enhances humeral shaft cortical bone properties in pre-pubertal baseball players: a 12-month longitudinal pilot study

Objectives: To explore throwing athletes as a prospective, within-subject controlled model for studying the response of the skeleton to exercise. Methods: Male pre-pubertal throwing athletes (n=12; age=10.3±0.6 yrs) had distal humerus cortical volumetric bone mineral density (Ct.vBMD), cortical bone mineral content (Ct.BMC), total area (Tt.Ar), cortical area (Ct.Ar), medullary area (Me.Ar), cortical thickness (Ct.Th) and polar moment of inertia (IP) assessed within their throwing (exercised) and nonthrowing (control) arms by peripheral quantitative computed tomography at baseline and 12 months. Throwing-to-nonthrowing arm percent differences (i.e. bilateral asymmetry) were compared over time. Results: Over 12 months, the throwing arm gained 4.3% (95% Cl=1.1% to 7.5%), 2.9% (95% Cl=0.3% to 5.4%), 3.9% (95% Cl=0.7% to 7.0%), and 8.2% (95% Cl=2.0% to 6.8%) more Ct.BMC, Ct.Ar, Tt.Ar, and IP than the nonthrowing arm, respectively (all p<0.05). There was no significant effect of throwing on Ct.vBMD, Ct.Th and Me.Ar (all p=0.18-0.82). Conclusion: Throwing induced surface-specific cortical bone adaptation at the distal humeral diaphysis that contributed to a gain in estimated strength. These longitudinal pilot data support the utility of throwing athletes as a within-subject controlled model to explore factors influencing exercise-induced bone adaptation during the critical growing years

Tibial Bone Strength is Enhanced in the Jump Leg of Collegiate-Level Jumping Athletes: A Within-Subject Controlled Cross-Sectional Study

An efficient method of studying skeletal adaptation to mechanical loading is to assess side-to-side differences (i.e., asymmetry) within individuals who unilaterally exercise one side of the body. Within-subject controlled study designs have been used to explore skeletal mechanoadaptation at upper extremity sites; however, there is no established model in the lower extremities. The current study assessed tibial diaphysis and distal tibia asymmetry in collegiate-level jumping athletes (N = 12). To account for normal crossed asymmetry, data in jumping athletes were compared to asymmetry in a cohort of athletic controls not routinely exposed to elevated unilateral lower extremity loading (N = 11). Jumpers exhibited side-to-side differences between their jump and lead legs at both the tibial diaphysis and distal tibia, with differences at the former site persisting following comparison to dominant-to-nondominant leg differences in controls. In particular, jump-to-lead leg differences for cortical area and thickness at the tibial diaphysis in jumpers were 3.6% (95% CI 0.5-6.8%) and 3.5% (95% CI 0.4-6.6%) greater than dominant-to-nondominant differences in controls, respectively (all p < 0.05). Similarly, jump-to-lead leg differences in jumpers for tibial diaphysis maximum second moment of area and polar moment of inertia were 7.2% (95% CI 1.2-13.2%) and 5.7% (95% CI 1.7-9.8%) greater than dominant-to-nondominant differences in controls, respectively (all p < 0.05). Assessment of region-specific differences of the tibial diaphysis in jumpers indicated that the jump leg had greater pericortical radii on the medial and posterior sides and greater radial cortical thickness posteromedially when compared to the lead leg. These data suggest that athletes who perform repetitive and forceful unilateral jumping may be a useful and efficient within-subject controlled model for studying lower extremity skeletal mechanoadaptation

Baseball and softball pitchers are distinct within-subject controlled models for exploring proximal femur adaptation to physical activity

Purpose: Within-subject controlled models in individuals who preferentially load one side of the body enable efficient exploration of the skeletal benefits of physical activity. There is no established model of physical activity-induced side-to-side differences (i.e., asymmetry) at the proximal femur. Methods: Proximal femur asymmetry was assessed via dual-energy x-ray absorptiometry in male jumping athletes (JMP, n=16), male baseball pitchers (BB, n=21), female fast-pitch softball pitchers (SB, n=22), and controls (CON, n=42). The jumping leg was the dominant leg in JMP, whereas in BB, SB and CON the dominant leg was contralateral to the dominant/throwing arm. Results: BB and SB had 5.5% (95%CI, 3.9 to 7.0%) and 6.5% (95%CI, 4.8 to 8.2%) dominant-to-nondominant leg differences for total hip areal bone mineral density (aBMD), with the asymmetry being greater than both CON and JMP (p8%) dominant-to-nondominant leg differences in cross-sectional area, cross-sectional moment of inertia and section modulus, which were larger than any other group (p≤0.02). Conclusion: Male baseball and female softball pitchers are distinct within-subject controlled models for exploring adaptation of the proximal femur to physical activity. They exhibit adaptation in their dominant/landing leg (i.e., leg contralateral to the throwing arm), but the pattern differs with softball pitchers exhibiting greater femoral neck adaptation

Cardiovascular responses during light-intensity aerobic exercise with varying levels of limb occlusion pressures.

International Journal of Exercise Science 16(2): 676-687, 2023. The study aimed to assess cardiovascular responses to low-intensity aerobic exercise with varying levels of limb occlusion pressures (LOP) in a healthy population of men and women 30 to 60 years. The study was a single-session repeated measures design. Thirty individuals completed the study. All subjects participated in a single bout of low-intensity cycling (30-39% HRR) with bilateral lower extremity (LE) BFR for four 5-minute stages [0% (No BFR), 40%, 60%, and 80% LOP] with a 2-minute active rest between stages (BFR pressure released). The subjects’ systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), heart rate (HR), oxygen saturation (SpO2), and ratings of perceived exertion (RPE) were measured at rest, peak, immediately post, post-15 minutes, and post-30 minutes. Peak SBP (no BFR 160.7 ±19.1 mmHg; 40% LOP 173.6 ± 18.7 mmHg; 60 % LOP; 182.5 ± 21.1 mmHg; 80% LOP 193.5± 23.3 mmHg ; p\u3c0.001; =.747), DBP (no BFR 74.9 ± 8.5 mmHg; 40% LOP (83.0 ± 9.0 mmHg;60 % LOP 90.4 ± 8.7 mmHg; 80% LOP 97.7 ± 9.5 mmHg ;p\u3c0.001; =.924), MAP (no BFR 103.5 ± 10.1 mmHg; 40% LOP 113.2 ± 10.5 mmHg; 60% LOP 121.1 ± 11.7 mmHg; 80% LOP 129.7 ± 12.9 mmHg; p\u3c0.001; =.960), and RPE (No BFR 10.0 ± 2.0; 40 % LOP 11.5 ± 2.3; 60% LOP 13.2 ± 2.6; 80% LOP 14.5 ± 3.; p\u3c0.001; =.826) were significantly higher with each progressing stage. The results indicate that low-intensity cycling with bilateral LE BFR for each LOP stage resulted in elevated SBP, DBP, MAP, and RPE despite maintaining a fixed HR

Progressive skeletal benefits of physical activity when young as assessed at the midshaft humerus in male baseball players

Physical activity benefits the skeleton, but there is contrasting evidence regarding whether benefits differ at different stages of growth. The current study demonstrates that physical activity should be encouraged at the earliest age possible and be continued into early adulthood to gain most skeletal benefits. INTRODUCTION: The current study explored physical activity-induced bone adaptation at different stages of somatic maturity by comparing side-to-side differences in midshaft humerus properties between male throwing athletes and controls. Throwers present an internally controlled model, while inclusion of control subjects removes normal arm dominance influences. METHODS: Throwing athletes (n = 90) and controls (n = 51) were categorized into maturity groups (pre, peri, post-early, post-mid, and post-late) based on estimated years from peak height velocity (10 years). Side-to-side percent differences in midshaft humerus cortical volumetric bone mineral density (Ct.vBMD) and bone mineral content (Ct.BMC); total (Tt.Ar), medullary (Me.Ar), and cortical (Ct.Ar) areas; average cortical thickness (Ct.Th); and polar Strength Strain Index (SSIP) were assessed. RESULTS: Significant interactions between physical activity and maturity on side-to-side differences in Ct.BMC, Tt.Ar, Ct.Ar, Me.Ar, Ct.Th, and SSIP resulted from the following: (1) greater throwing-to-nonthrowing arm differences than dominant-to-nondominant arm differences in controls (all p < 0.05) and (2) throwing-to-nonthrowing arm differences in throwers being progressively greater across maturity groups (all p < 0.05). Regional analyses revealed greatest adaptation in medial and lateral sectors, particularly in the three post-maturity groups. Years throwing predicted 59% of the variance of the variance in throwing-to-nonthrowing arm difference in SSIP (p < 0.001). CONCLUSION: These data suggest that physical activity has skeletal benefits beginning prior to and continuing beyond somatic maturation and that a longer duration of exposure to physical activity has cumulative skeletal benefits. Thus, physical activity should be encouraged at the earliest age possible and be continued into early adulthood to optimize skeletal benefits

Achilles tendon material properties are greater in the jump leg of jumping athletes

Purpose: The Achilles tendon (AT) must adapt to meet changes in demands. This study explored AT adaptation by comparing properties within the jump and non-jump legs of jumping athletes. Non-jumping control athletes were included to control limb dominance effects. Methods: AT properties were assessed in the preferred (jump) and non-preferred (lead) jumping legs of male collegiate-level long and/or high jump (jumpers; n=10) and cross-country (controls; n=10) athletes. Cross-sectional area (CSA), elongation, and force during isometric contractions were used to estimate the morphological, mechanical and material properties of the ATs bilaterally. Results: Jumpers exposed their ATs to more force and stress than controls (all p≤0.03). AT force and stress were also greater in the jump leg of both jumpers and controls than in the lead leg (all p0.05). Conclusion: ATs chronically exposed to elevated mechanical loading were found to exhibit greater mechanical (stiffness) and material (Young’s modulus) properties

EFFECTS OF KAATSU TRAINING ON UPPER EXTREMITY SIZE AND STRENGTH

poster abstractConventional resistance training involves lifting heavy loads (~70% max-imal strength), which can be poorly tolerated or contraindicated in many clinical populations. KAATSU training is a novel training mode from Japan that combines muscle blood flow restriction with low load lifting (~20% max-imal strength). The purpose of this study was to investigate the effects of a KAATSU training program on upper extremity size and strength. Forty healthy subjects ages 18 to 30 were divided into exercise (EX) or control (CON) groups. Subjects reported to the laboratory three times per week for eight weeks. The EX group performed 3 sets of 15 repetitions of unilateral bicep curls and triceps extensions lifting loads equivalent to 20% of their predetermined maximal strength while wearing a pneumatic cuff to restrict blood flow on one arm (CUFF) and nothing on the other (NCUFF). The CON group did not perform any exercises but wore the cuff on one arm for a time comparable to the EX group. CUFF and NCUFF arms were randomly as-signed. Strength, girth, skin folds and tomography scans were taken pre-, during, and post-eight weeks. In the EX group, bicep curl (17.4% +4.1% and 18.7% +4.9%) and triceps extension (15.8% +3.4% and 10.7% +2.7%) strength increased significantly over the 8-week period for both the CUFF and NCUFF arms, respectively. No significant differences in strength occurred between the CUFF and NCUFF arms within the group. No strength changes were noted in the CON group for the CUFF and NCUFF arms. Arm girth and muscle cross-sectional area (mCSA) increased significantly in the EX subjects compared to the CON subjects, however no significant differ-ences were found when within group comparisons were made between the CUFF and NCUFF arms. This study indicates that KAATSU training can in-crease muscle strength and mCSA

KAATSU TRAINING: PERCEPTIONS AND COMPLIANCE TO AN UPPER ARM EXERCISE PROGRAM

poster abstractKAATSU training is a novel Japanese training mode involving low load (~20% maximal strength) weightlifting combined with blood flow restriction to the muscles. Little is known about the sensations experienced during KAATSU training and whether clients will tolerate it. The purpose of this study was to assess perceived sensations, exertion rates, and compliance to an upper arm KAATSU training program. Forty healthy subjects ages 18 to 30 were divided into exercise (EX) or control (CON) groups. Subjects report-ed to the laboratory three times per week for eight weeks. The EX group performed 3 sets of 15 repetitions of unilateral bicep curls and triceps exten-sions lifting loads equivalent to 20% of their predetermined maximal strength while wearing a pneumatic cuff on one arm (CUFF) and nothing on the other (NCUFF). The CON group did not perform any exercises but wore the cuff on one arm for a time comparable to the EX group. CUFF and NCUFF arms were randomly assigned. Sensations (burning, aching, pressure, pins & needles) and perceived exertion were assessed using visual analog scales that included emotions and verbal cues. Compliance (percentage of subjects completing the pre- and post-testing) and adherence (percentage of ses-sions completed) were tracked to provide an indication of training tolerance. Compliance was 85.4% and 97% for the EX and CON groups, respectively. EX subjects completed 85.4% of their workouts while controls attended 90.4% of their sessions. The prominent sensation reported in the CUFF arm was pressure (moderate; 3.2 +0.6) followed by aching (weak; 1.7 +0.4). Ratings of perceived exertion were higher for the CUFF (3.2 +1.0, 5.1 +1.8, and 7.0 +2.5) versus NCUFF (1.5 +0.3, 2.4 +0.3, and 3.3 +0.4) arm for sets 1, 2, and 3, respectively. KAATSU training is well tolerated by those performing it and a viable alternative to conventional resistance exercise

Peripheral quantitative computed tomography (pQCT) predicts humeral diaphysis torsional mechanical properties with good short-term precision.

Peripheral quantitative computed tomography (pQCT) is a popular tool for non-invasively estimating bone mechanical properties. Previous studies have demonstrated pQCT provides precise estimates that are good predictors of actual bone mechanical properties at popular distal imaging sites (tibia and radius). The predictive ability and precision of pQCT at more proximal sites remains unknown. The aim of the current study was to explore the predictive ability and short-term precision of pQCT estimates of mechanical properties of the midshaft humerus, a site gaining popularity for exploring the skeletal benefits of exercise. Predictive ability was determined ex vivo by assessing the ability of pQCT-derived estimates of torsional mechanical properties in cadaver humeri (density-weighted polar moment of inertia [IP] and polar Strength Strain Index [SSIP]) to predict actual torsional properties. Short-term precision was assessed in vivo by performing six repeat pQCT scans at the level of the midshaft humerus in 30 young, healthy individuals (degrees of freedom = 150), with repeat scans performed by the same and different testers and on the same and different days to explore the influences of different testers and time between repeat scans on precision errors. IP and SSIP both independently predicted at least 90% of the variance in ex vivo midshaft humerus mechanical properties in cadaveric bones. Overall values for relative precision error (root mean squared coefficients of variation) for in vivo measures of IP and SSIP at the midshaft humerus were less than 1.5% and were not influenced by pQCT assessments being performed by different testers or on different days. These data indicate that pQCT provides very good prediction of midshaft humerus mechanical properties with good short-term precision, with measures being robust against the influences of different testers and time between repeat scans

Heterogeneous Spatial and Strength Adaptation of the Proximal Femur to Physical Activity: A Within-Subject Controlled Cross-Sectional Study

Physical activity (PA) enhances proximal femur bone mass, as assessed using projectional imaging techniques. However, these techniques average data over large volumes obscuring spatially heterogeneous adaptations. The current study used quantitative computed tomography, statistical parameter mapping, and subject-specific finite element (FE) modeling to explore spatial adaptation of the proximal femur to PA. In particular, we were interested in adaptation occurring at the superior femoral neck and improving strength under loading from a fall onto the greater trochanter. High/long jump athletes (n=16) and baseball pitchers (n=16) were utilized as within-subject controlled models as they preferentially load their takeoff leg and leg contralateral to their throwing arm, respectively. Controls (n=15) were included, but did not show any dominant-to-nondominant (D-to-ND) leg differences. Jumping athletes showed some D-to-ND leg differences, but less than pitchers. Pitchers had 5.8% (95% CI, 3.9–7.6%) D-to-ND leg differences in total hip volumetric bone mineral density (vBMD), with increased vBMD in the cortical compartment of the femoral neck, and trochanteric cortical and trabecular compartments. Voxel-based morphometry analyses and cortical bone mapping showed pitchers had D-to-ND leg differences within the regions of the primary compressive trabeculae, inferior femoral neck, and greater trochanter, but not the superior femoral neck. FE modeling revealed pitchers had 4.1% (95%CI, 1.4–6.7%) D-to-ND leg differences in ultimate strength under single-leg stance loading, but no differences in ultimate strength to a fall onto the greater trochanter. These data indicate the asymmetrical loading associated with baseball induces proximal femur adaptation in regions associated with weight bearing and muscle contractile forces, and increases strength under single-leg stance loading. However, there were no benefits evident at the superior femoral neck and no measurable improvement in ultimate strength to common injurious loading during aging (i.e. fall onto the greater trochanter) raising questions as to how to better target these variables with PA