Examining the role of different weakness categories for mobility and future falls in older Americans.

BACKGROUND: Recently developed absolute and body size normalized handgrip strength (HGS) cut-points could be used individually and collectively to predict mobility problems and falls. AIMS: We examined the associations of (1) each absolute and normalized weakness cut-point, (2) collective weakness categories, and (3) changes in weakness status on future falls in older Americans. METHODS: The analytic sample included 11,675 participants from the 2006-2018 waves of the Health and Retirement Study. Falls were self-reported. Men were classified as weak if their HGS was < 35.5-kg (absolute), < 0.45 kg/kg (body mass normalized), or < 1.05 kg/kg/m2 (body mass index normalized). While, women were considered weak if their HGS was < 20.0-kg, < 0.337 kg/kg, or < 0.79 kg/kg/m2. Collective weakness categorized those below 1, 2, or all 3 cut-points. The collective weakness categories were also used to observe changes in weakness status over time. RESULTS: Older Americans below each absolute and normalized cut-point had greater odds for future falls: 1.23 (95% confidence interval (CI): 1.15-1.32) for absolute weakness, 1.20 (CI 1.11-1.29) for body mass index normalized weakness, and 1.26 (CI 1.17-1.34) for body mass normalized weakness. Persons below 1, 2, or all 3 weakness cut-points had 1.17 (CI 1.07-1.27), 1.29 (CI 1.18-1.40), and 1.36 (CI 1.24-1.48) greater odds for future falls, respectively. Those in some changing weakness categories had greater odds for future falls: 1.26 (CI 1.08-1.48) for persistent and 1.31 (CI 1.11-1.55) for progressive. DISCUSSION: Collectively using these weakness cut-points may improve their predictive value. CONCLUSION: We recommend HGS be evaluated in mobility and fall risk assessments.

Using Electronic Handgrip Dynamometry and Accelerometry to Examine Multiple Aspects of Handgrip Function in Master Endurance Athletes: A Pilot Study.

ABSTRACT: Klawitter, LA, Hackney, KJ, Christensen, BK, Hamm, JM, Hanson, M, and McGrath, R. Using electronic handgrip dynamometry and accelerometry to examine multiple aspects of handgrip function in master endurance athletes: A Pilot Study. J Strength Cond Res 37(9): 1777-1782, 2023-Electronic handgrip dynamometry and accelerometry may provide novel opportunities to comprehensively measure muscle function for human performance, especially for master athletes. This investigation sought to determine the multivariate relationships between maximal strength, asymmetry, rate of force development, fatigability, submaximal force control, bimanual coordination, and neuromuscular steadiness to derive one or more handgrip principal components in master-aged endurance athletes. We included n = 31 cyclists and triathletes aged 35-70 years. Maximal strength, asymmetry, rate of force development, fatigability, submaximal force control, bimanual coordination, and neuromuscular steadiness were measured twice on each hand using electronic handgrip dynamometry and accelerometry. The highest performing measures were included in the analyses. A principal component analysis was conducted to derive a new collection of uncorrelated variables from the collected handgrip measurements. Principal components with eigenvalues >1.0 were kept, and individual measures with a factor loading of |>0.40| were retained in each principal component. There were 3 principal components retained with eigenvalues of 2.46, 1.31, and 1.17. The first principal component, "robust strength," contained maximal strength, rate of force development, submaximal force control, and neuromuscular steadiness. The second principal component, "bilateral synergy," contained asymmetry and bimanual coordination, whereas the third principal component, "muscle conditioning," contained fatigability. Principal components 1, 2, and 3 explained 44.0, 31.6, and 24.4% of the variance, respectively. Different dimensions of muscle function emerged from our findings, suggesting the potential of a muscle function battery. Further research examining how these measures are associated with appropriate human performance metrics and lower extremity correlates is warranted.

Prevalence and Trends of Weakness Among Middle-Aged and Older Adults in the United States.

ABSTRACT: McGrath, R, FitzSimmons, S, Andrew, S, Black, K, Bradley, A, Christensen, BK, Collins, K, Klawitter, L, Kieser, J, Langford, M, Orr, M, and Hackney, KJ. Prevalence and trends of weakness among middle-aged and older adults in the United States. J Strength Cond Res 37(12): 2484-2490, 2023-Muscle weakness, which is often determined with low handgrip strength (HGS), is associated with several adverse health conditions; however, the prevalence and trends of weakness in the United States is not well-understood. We sought to estimate the prevalence and trends of weakness in Americans aged at least 50 years. The total unweighted analytic sample included 22,895 Americans from the 2006-2016 waves of the Health and Retirement Study. Handgrip strength was measured with a handgrip dynamometer. Men with weakness were below at least one of the absolute or normalized (body mass, body mass index) cut points: <35.5 kg, <0.45 kg/kg, <1.05 kg/kg/m 2 . The presence of any weakness in women was also identified as being below one of the absolute or normalized HGS cut points: <20.0 kg, <0.34 kg/kg, or <0.79 kg/kg/m 2 . There was an increasing trend in the prevalence of any weakness over time ( p < 0.001). The prevalence of weakness was 45.1% (95% confidence interval [CI]: 44.0-46.0) in the 2006-2008 waves and 52.6% (CI: 51.5-53.7) in the 2014-2016 waves. Weakness prevalence was higher for older (≥65 years) Americans (64.2%; CI: 62.8-65.5) compared with middle-aged (50-64 years) Americans (42.2%; CI: 40.6-43.8) in the 2014-2016 waves. Moreover, the prevalence of weakness in the 2014-2016 waves was generally higher in women (54.5%; CI: 53.1-55.9) than in men (50.4%; CI: 48.7-52.0). Differences existed in weakness prevalence across races and ethnicities. The findings from our investigation suggest that the prevalence of weakness is overall pronounced and increasing in Americans. Efforts for mitigating and better operationalizing weakness will elevate in importance as our older American population grows.

Differences in Muscle Activity and Kinetics Between the Goblet Squat and Landmine Squat in Men and Women.

ABSTRACT: Collins, KS, Klawitter, LA, Waldera, RW, Mahoney, SJ, and Christensen, BK. Differences in muscle activity and kinetics between the goblet squat and landmine squat in men and women. J Strength Cond Res 35(10): 2661-2668, 2021-Squat exercise variations are widely used and extensively researched. However, little information exists on the goblet squat (GBS) and landmine squat (LMS) and differences between men and women. This study investigated the differences in muscle activity and kinetics between the GBS and the LMS in 16 men and 16 women. Five repetitions of each squat type were performed loaded at 30% of their body mass. Vertical and anteroposterior ground reaction forces for the eccentric and concentric phases and peak vertical force were recorded with a force plate. Electromyographic (EMG) signals were recorded for the vastus medialis (VM), vastus lateralis (VL), semitendinosus (ST), and biceps femoris (BF). Normalized mean EMG values and ground reaction forces were analyzed with repeated measures analysis of variance (p < 0.05). Significant main effects for squat condition and sex were found. The LMS reduced activity in the quadriceps (VM and VL) muscles and vertical forces, while increasing posterior horizontal forces. In the LMS, men showed decreased ST activity, whereas women had decreased BF activity. Women exhibited greater quadriceps activity in both the GBS and LMS and greater ST in the LMS. Women also produced greater eccentric vertical force in both the GBS and LMS and less posterior horizontal forces in the LMS. The LMS may be useful to balance hamstring to quadriceps activity, increase horizontal loading, and reduce vertical loading. Conversely, the GBS can better target quadriceps activity and increase vertical loading. Sex differences should be considered for training programs that include the GBS and LMS.

Increased velocity at VO2max and load carriage performance in army ROTC cadets: prescription using the critical velocity concept.

The purpose of this study was to evaluate the effects of using the critical velocity (CV) concept to prescribe two separate high-intensity interval training (HIT) exercise programs aimed at enhancing CV and load carriage performance. 20 young adult participants (male = 15, female = 5) underwent a 4-week training period where they exercised 2 d wk-1. Participants were randomly assigned into two groups: (1) HIT or (2) Load Carriage-HIT (LCHIT). Pre- and post-training assessments included running 3-minute All-Out Test (3MT) to determine critical velocity (CV) and distance prime (D') and two load carriage tasks (400 and 3200 m). There were significant increases in CV (p = 0.005) and velocity at V˙ O2max (vV˙ O2max) (p = 0.037) among the sample but not between training groups. Improvements were observed in 3200 m load carriage performance time (p < 0.001) with a 9.8 and 5.4% decrease in the LCHIT and HIT groups, respectively. Practitioner summary: Critical velocity has shown efficacy as a marker for performance in tactical populations. With the addition of load carriage, there is a reduction in the individual's CV. The CV-concept-prescribed exercises (HIT and LCHIT) 2 days per week for 4 weeks showed improvements in CV, vV˙ O2max and load carriage performance. The use of the CV concept provides a method to prescribe HIT to increase running and load carriage performances in tactical populations.

Effect of Progressive Calisthenic Push-up Training on Muscle Strength and Thickness.

Kotarsky, CJ, Christensen, BK, Miller, JS, and Hackney, KJ. Effect of progressive calisthenic push-up training on muscle strength and thickness. J Strength Cond Res 32(3): 651-659, 2018-Calisthenics, a form of resistance training, continue to increase in popularity; however, few studies have examined their effectiveness for muscle strength improvement. The purpose of this study was to determine whether progressive calisthenic push-up training (PUSH) is comparable with traditional bench press training (BENCH) as a technique for increasing muscle strength and thickness. Twenty-three healthy, moderately trained men (mean ± SD: age 23 ± 6.8 years) completed the study. Subjects were randomly assigned to PUSH (n = 14) and BENCH (n = 9) groups and were trained 3 days per week for 4 weeks. Muscle thickness (MT), seated medicine ball put (MBP), 1 repetition maximum (1RM) bench press, and push-up progression (PUP) were measured before and after training. Results revealed significant increases in 1RM (p < 0.001) and PUP (p < 0.001) for both groups after training. The increase in PUP was significantly greater for PUSH (p < 0.001). No significant differences were found within groups for MT and MBP (p > 0.05). This study is the first to demonstrate that calisthenics, using different progressive variations to maintain strength training programming variables, can improve upper-body muscle strength.

Bench Press Range-of-Motion and Velocity-based Repetition Control: Effects on Ballistic Push-up Performance in Males.

The purpose of this study was to investigate whether the ballistic push-up (BPU) is responsive to post-activation performance enhancement (PAPE) after a bench press conditioning exercise using velocity-based repetition control. Additionally, we aimed to evaluate the effects of range of motion (ROM) conditions on subsequent BPU performance. In a randomized crossover design, 18 males performed two conditions (full ROM and self-selected partial ROM) of bench press at 80% of their 1RM until mean concentric velocity dropped 10%. Each participant performed two pre- and six post-test BPUs to assess the PAPE effect. Paired sample t-tests assessed bench press performance measures. Multiple two-way repeated measures ANOVAs assessed differences in flight time, impulse, and peak power for the pre- and post-test BPUs. No significant differences existed between ROM conditions for total repetitions, volume load, or peak velocity. Compared to partial ROM, full ROM showed greater displacement (0.42 ± 0.05 vs. 0.34 ± 0.05 m), work (331.99 ± 67.72 vs. 270.92 ± 61.42 J), and mean velocity (0.46 ± 0.09 vs. 0.44 ± 0.08 m/s). Neither bench press ROM condition enhanced the BPU and were detrimental in some cases. Several time points showed partial ROM (flight time: 2 min post, impulse: 12 min post, peak power: 12 min post) significantly greater than full ROM, possibly indicating less fatigue accumulation. The BPU may require a different stimulus or may not be practical for PAPE effects in college-aged males. Partial ROM can be an alternative that achieves similar peak velocities while requiring less overall work.

The Association Between Handgrip Strength Asymmetry Severity and Future Morbidity Accumulation: Results from the Health and Retirement Study.

Analyzing the severity of handgrip strength (HGS) asymmetry in aging populations may help to screen for morbidities and add utility to handgrip dynamometer testing. Our study sought to determine the relationships between HGS asymmetry severity and future accumulating morbidities in older Americans. Secondary analyses from the 2006-2016 waves of the Health and Retirement Study included 18,506 adults ≥ 50 years old. The highest recorded HGS values from each hand were used to calculate HGS asymmetry ratio (non-dominant HGS/dominant HGS). If the HGS asymmetry ratio < 1.0, it was inversed to make all asymmetry ratios ≥ 1.0. Participants were categorized into groups based on the severity of their HGS asymmetry ratio: 1) 0.0% - 10.0%, 2) 10.1% - 20.0%, 3) 20.1% - 30.0%, and 4) > 30.0%. Healthcare provider-diagnosed morbidities (hypertension, diabetes, cancer, chronic lung disease, cardiovascular disease, stroke, arthritis, and psychiatric problems) were self-reported. Covariate-adjusted ordinal generalized estimating equations evaluated the relationships between HGS asymmetry severity on future accumulating morbidities. Results showed 8,936 (48.3%) participants had HGS asymmetry 0.0%-10.0%, 6,105 (33.0%) participants had HGS asymmetry 10.1%-20.0%, 2,411 (13.0%) participants had HGS asymmetry 20.1%-30.0%, and 1,054 (5.7%) participants had HGS asymmetry > 30.0%. Overall, every 10% increase in HGS asymmetry was associated with a 1.17 (CI: 1.05, 1.32) greater odds of future morbidity accumulation. Additionally, asymmetry between 10.1% - 20.0%, 20.1% - 30.0%, and > 30.0% was associated with a 1.10 (CI: 1.05, 1.15), 1.11 (CI: 1.04, 1.18), and 1.20 (CI: 1.09, 1.33) greater odds for morbidity accumulation during aging. These findings suggest that severe functional asymmetries may elevate the odds for accumulating morbidities.

Analysis of Total and Segmental Body Composition Relative to Fitness Performance Measures in Law Enforcement Recruits.

Law enforcement agencies often test the fitness performance and body composition of incoming recruits. This study investigated the relationships between whole and segmental body composition, and fitness tests in law enforcement recruits. A retrospective analysis of 72 male and 11 female recruits was performed. Bioelectrical impedance analysis (BIA) variables were: lean mass (LM), upper-extremity lean mass (UELM), trunk LM, lower-extremity lean mass (LELM), fat mass (FM), upper-extremity fat mass (UEFM), trunk FM, and lower-extremity fat mass (LEFM). Fitness tests included: vertical jump (VJ), peak anaerobic power (PAPw), 75-yard pursuit run (75PR), push-ups, sit-ups, 2-kg medicine ball throw (MBT), and the multi-stage fitness test (MSFT). Partial correlations and ANCOVAs between quartiles assessed relationships between body composition and performance. Significant moderate-to-large relationships were found; LM, UELM, trunk LM, LELM all related to PAPw (r = 0.500-0.558) and MBT (r = 0.494-0.526). FM, UEFM, trunk FM, LEFM all related to VJ (r = -0.481 to -0.493), 75PR (r = 0.533-0.557), push-ups (r = -0.484 to -0.503), sit-ups (r = -0.435 to -0.449), and MSFT (r = -0.371 to -0.423). The highest LM quartile (4) had superior PAPw and MBT than LM quartiles 1-3. Higher FM quartiles performed poorer in VJ, push-ups, and sit-ups. The 75PR quartiles 2, 3, and 4 were slower than quartile 1, and MSFT quartile 4 completed less shuttles. Total and segmental measures of LM and FM shared the same relationships; lower FM and higher LM related to better performance. Monitoring body composition could help guide training to optimize performance.

The Associations between Asymmetric Handgrip Strength and Chronic Disease Status in American Adults: Results from the National Health and Nutrition Examination Survey.

This study examined the associations between asymmetric handgrip strength (HGS) and multimorbidity in American adults. Secondary analyses of data from persons aged at least 40 years from the 2011-2012 and 2013-2014 waves of the National Health and Nutrition Examination Survey were conducted. A handheld dynamometer collected HGS on each hand and persons with a strength imbalance >10% between hands were classified as having asymmetric HGS. Adults with the presence of ≥2 of the following conditions had multimorbidity: cardiovascular disease, chronic obstructive pulmonary disease, chronic kidney disease, asthma, arthritis, cancer, obesity, stroke, hypertension, high cholesterol, and diabetes. Of the n = 3483 participants included, n = 2700 (77.5%) had multimorbidity. A greater proportion of adults with multimorbidity had HGS asymmetry (n = 1234 (45.7%)), compared to persons living without multimorbidity (n = 314 (40.1%); p < 0.05). Relative to individuals without asymmetry, adults with asymmetric HGS had 1.31 (95% confidence interval (CI): 1.03-1.67) greater odds for multimorbidity. Moreover, persons with HGS asymmetry had 1.22 (CI: 1.04-1.44) greater odds for accumulating morbidities. Asymmetric strength, as another indicator of diminished muscle function, is linked to chronic morbidity status. Healthcare providers should recommend healthy behaviors for reducing asymmetries to improve muscle function and mitigate morbidity risk after completing asymmetry screenings.

Simulated Casualty Evacuation Performance Is Augmented by Deadlift Peak Force.

INTRODUCTION: The purpose of the current study was to examine if isometric peak force and rate of force development (RFD) were related to the ability to successfully perform a simulated casualty evacuation task in both unweighted and weighted conditions. METHODS: Eighteen male participants from Army Reserve Officers' Training Corps (ROTC) completed a maximum isometric deadlift on a force plate (IRB#HE16227). Isometric peak force and RFD were calculated from ground reaction force. Two simulated casualty evacuation performance trials were then completed. The unweighted trial consisted of lifting and carrying a 75 kg dummy as quickly as possible for 50 m. The weighted trial was similar except 9 kg vests were added to both the simulation dummy and the participant to represent 18 kg of duty gear. Independent sample t-tests and Pearson correlations were performed to compare the characteristics of those who passed and failed the weighted trial. RESULTS: All of the participants (n = 18) completed the unweighted casualty evacuation trial, while 72% (n = 13) were able to complete the weighted casualty evacuation trial. The participants that successfully completed the weighted evacuation trial had significantly (p < 0.05) greater isometric peak force (1420 ± 165 vs. 1076 ± 256 N) and lean mass (74.18 ± 3.89 vs. 65.34 ± 3.89 kg) when compared to participants (n = 5) that could not complete the weighted evacuating task trial. Additionally, greater Army Physical Fitness Test scores (288 ± 13 vs. 269 ± 16 arbitrary units) and significantly faster (30.34 ± 4.41 vs. 44.92 ± 10.62 seconds) unweighted evacuation trial times were observed in participants that could complete the weighted evacuation task. Peak force was also significantly correlated with lean mass (r = 0.51, p < 0.05). There was no relationship between RFD and performance of the unweighted or weight trial. CONCLUSION: Isometric deadlift peak force represents an important determinant for the success of a simulated casualty evacuation task and may be a useful marker to include in periodic fitness evaluations of military personnel.

Acute Cardiovascular, Metabolic, and Muscular Responses to Blood Flow Restricted Rowing Exercise.

INTRODUCTION: Microgravity leads to a progressive loss in muscular strength, endurance, and aerobic capacity (Vo2peak). Blood flow restricted (BFR) exercise has been shown to elicit rapid gains in muscular strength and Vo2peak. Rowing exercise combined with BFR could be a supplemental countermeasure to maintain preflight muscle function and Vo2peak, especially within future space vehicles with restricted physical volume.METHODS: There were 20 men who completed 19 min of rowing exercise during CON or BFR in a randomized order. Exercise intensity for all sets was 30% of peak work load achieved during a separate incremental maximal exercise test. Kaatsu training cuffs were inflated around each leg during BFR. Muscle oxygen saturation (Smo2) and heart rate (HR) were measured throughout exercise and rest. Rate of perceived exertion (RPE) and muscle activation, using surface electromyography (sEMG), were measured during the last 30 s of each exercise set. Blood pressure (BP) and whole blood lactate ([La-]b) were measured at rest and postexercise.RESULTS: Smo2 declined significantly in BFR during exercise and rest by 13% and 14%, respectively. HR and RPE showed significant increases during BFR (120.5 ± 5.53 vs. 128.9 ± 9.86 bts · min-1) (9.8 ± 1.85 vs. 11.8 ± 1.88 arbitrary units). No differences were observed for BP, [La-]b, and sEMG.DISCUSSION: Findings indicate exercise intensity and cuff pressure elicited acute muscular, cardiovascular, and perceptual responses. BFR rowing exercise could be advantageous as an adjunct for future exercise countermeasures where aerobic and anaerobic exercise may be performed on one device or in limited physical space.Mahoney SJ, Dicks ND, Lyman KJ, Christensen BK, Hackney KJ. Acute cardiovascular, metabolic, and muscular responses to blood flow restricted rowing exercise. Aerosp Med Hum Perform. 2019; 90(5):440-446.

The effects of proprioceptive neuromuscular facilitation and dynamic stretching techniques on vertical jump performance.

The purpose of this study was to investigate the effects of 3 different warm-ups on vertical jump performance. The warm-ups included a 600-m jog, a 600-m jog followed by a dynamic stretching routine, and a 600-m jog followed by a proprioceptive neuromuscular facilitation (PNF) routine. A second purpose was to determine whether the effects of the warm-ups on vertical jump performance varied by gender. Sixty-eight men and women NCAA Division I athletes from North Dakota State University performed 3 vertical jumps on a Just Jump pad after each of the 3 warm-up routines. The subjects were split into 6 groups and rotated between 3 warm-up routines, completing 1 routine each day in a random order. The results of the 1-way repeated measures analysis of variance showed no significant differences in the combined (p = 0.927), men's (p = 0.798), or women's (p = 0.978) results. The results of this study showed that 3 different warm-ups did not have a significant affect on vertical jumping. The results also showed there were no gender differences between the 3 different warm-ups.

Biomechanical analysis of women weightlifters during the snatch.

The majority of the research to date on weightlifting has focused on men competitors. This study attempted to bridge the sex-based gap evident in the scientific literature. The performances of 10 women weightlifters competing in the 1999 United States national championships were analyzed. The performance of the athletes competing in the 69-kg class was recorded and analyzed using a Peak5 2D Motion Analysis system. The purpose of this study was 3-fold: (a) analyze the horizontal bar displacement of women weightlifters, (b) analyze key kinematic variables related to performance, and (c) compare the power outputs of the first, second, and total pulls in the snatch. Less than half (<50%) of the snatch attempts demonstrated by the women weightlifters in this study displayed the optimal toward-away-toward horizontal bar trajectory reported elsewhere. The women in this study demonstrated greater drop displacement and drop under times than those previously reported for men weightlifters. They also demonstrated lesser maximal vertically velocities of the barbell than those reported for world class women weightlifters. These women weightlifters demonstrated statistically significant differences (p < 0.05) during each phase of the snatch, and total power output values were comparable to values previously reported. The results of this study suggest that women demonstrate performance characteristics that differ subtly from those reported in men weightlifters. Knowledge of performance measures during the snatch may help coaches and athletes more fully refine the training leading to competition.