Recommendations for endurance exercise prescription are often based on percentages of heart rate ... more Recommendations for endurance exercise prescription are often based on percentages of heart rate (HR) or the volume of oxygen consumption ( . VO 2 ) maximum or reserve that is extrapolated to a power output (P) or velocity. Previous work has demonstrated dissociations of the expected responses to exercise anchored to the critical heart rate (CHR) compared with the P associated with CHR. However, it is unclear if similar dissociations due to reductions in P to maintain the designated intensity would be present during exercise anchored to the . VO 2 associated with CHR ( . VO 2 CHR). The purpose of this study was to examine the patterns in physiological ( . VO 2 , HR, P, respiration rate [RR], muscle oxygen saturation [%SmO 2 ]), neuromuscular (electromyographic and mechanomyographic amplitude [EMG AMP, MMG AMP], mean power frequency [EMG MPF, MMG MPF]), and perceptual (rating of perceived exertion [RPE]) responses during exercise at . VO 2 CHR ( . VO 2 -clamp). On separate days, ten participants (age: 25 ± 4 yr) performed a graded exercise test and four constant P trials at 85-100% of peak P (PP) to derive CHR and . VO 2 CHR. Responses were recorded during a trial to exhaustion at . VO 2 CHR (32.86 ± 7.12 mL•kg -1 •min -1 ; T Lim = 31.31 ± 21.37 min) and normalized in 10% intervals of T Lim to their respective values at PP. The one-way repeated-measures ANOVA with post hoc, Bonferroni-corrected, pairwise comparisons indicated differences (p < 0.001) from baseline for HR (mean ± SD %change = 8 ± 3%), RR (43 ± 38%), P (-15 ± 5%), EMG MPF (10 ± 8%), and RPE (65 ± 38%), but no differences (p = 0.077-0.955) for %SmO 2 (-17 ± 53%), EMG AMP (-3 ± 16%), MMG AMP (40 ± 61%), and MMG MPF (1 ± 7%). The loss in performance observed during . VO 2 -Clamp exercise may provide a quantification of the inefficiency associated with the . VO 2 slow component phenomenon. The neuromuscular responses suggested constant muscle excitation despite the reductions in P, but the metabolic and perceptual responses suggested a combination of feedforward and feedback mechanisms regulating T Lim . Future studies should further examine responses to the . VO 2 -Clamp exercise at a uniform threshold.
The prevalence of hypertension is increasing particularly among obese children and adolescents. O... more The prevalence of hypertension is increasing particularly among obese children and adolescents. Obese children and adolescents with hypertension are likely to remain hypertensive as they reach adulthood and hypertension is linked to an increased risk for cardiovascular disease. Twenty-four-hour ambulatory blood pressure monitoring (ABPM) has become one of the most important tools in diagnosing hypertension in children and adolescents and circadian patterns of blood pressure may be important disease-risk predictors. Methods: A retrospective chart review was conducted in patients aged 6-21 years who underwent 24-h ABPM at Kentucky Children's Hospital (KCH) from August 2012 through June 2017. Exclusion criteria included conditions that could affect blood pressure including chronic kidney disease and other renal abnormalities, congenital heart disease, cancer, and thyroid disease. Subjects were categorized by body mass index into normal (below 85th percentile), overweight (85th-95th percentile), stage I obesity (95th-119th percentile), stage II obesity (120th-139th) and stage III obesity (>140th). Non-dipping was defined as a nocturnal BP reduction of <10%. Results: Two hundred and sixty-three patients (156 male patients) were included in the analysis, of whom 70 were normal weight, 33 overweight, 55 stage I obesity, 53 stage II, and 52 stage III obesity. Although there was no significant difference between normal weight and obese groups for prevalence of hypertension, there was a greater prevalence of SBP non-dipping in obese patients as BMI increased (p = 0.008). Furthermore, non-dippers had a significantly elevated LVMI as well as abnormal lab values for uric acid, blood lipid panel, creatinine, and TSH (p < 0.05). Conclusions: These findings demonstrate that obese children and adolescents constitute a large proportion of hypertensive children and adolescents and the severity of pediatric obesity is associated with nocturnal BP non-dipping. Additionally, obesity in children is linked to several cardiovascular risk factors including left ventricular hypertrophy, dyslipidemia, and elevated uric acid levels. Further studies utilizing ABPM measures on risk stratification in this very high-risk population are warranted.
Journal of Strength and Conditioning Research, Jul 1, 2019
Dinyer, TK, Byrd, MT, Garver, MJ, Rickard, AJ, Miller, WM, Burns, S, Clasey, JL, and Bergstrom, H... more Dinyer, TK, Byrd, MT, Garver, MJ, Rickard, AJ, Miller, WM, Burns, S, Clasey, JL, and Bergstrom, HC. Low-load vs. high-load resistance training to failure on one repetition maximum strength and body composition in untrained women. J Strength Cond Res 33(7): 1737-1744, 2019-This study examined the effects of resistance training (RT) to failure at low and high loads on one repetition maximum (1RM) strength and body composition (bone-and fat-free mass [BFFM] and percent body fat [%BF]) in untrained women. Twenty-three untrained women (age: 21.2 6 2.2 years; height: 167.1 6 5.7 cm; body mass: 62.3 6 16.2 kg) completed a 12-week RT to failure intervention at a low (30% 1RM) (n 5 11) or high (80% 1RM) (n 5 12) load. On weeks 1, 5, and 12, subjects completed 1RM testing for 4 different exercises (leg extension [LE], seated military press [SMP], leg curl [LC], and lat pull down [LPD]) and a dual-energy x-ray absorptiometry scan to assess body composition. During weeks 2-4 and 6-7, the subjects completed 2 sets to failure for each exercise. During weeks 8-11, the subjects completed 3 sets to failure for each exercise. The 1RM strength increased from week 1 to week 5 (LE:
261 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1993.The influence of high and ... more 261 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1993.The influence of high and low levels of physical activity on bone mineral content (BMC) and bone mineral density (BMD) was investigated in 60 healthy, Caucasian, early postmenopausal women. All women examined were a minimum of two but no more than five years past natural menstrual cessation. Subjects in the high physical activity group (n = 30) had an energy expenditure greater than 3000 kcal/week and in the low physical activity group (n = 30) less than 1500 kcal/week, estimated from walking, stair climbing, and sport and recreational activity participation. The physical activity groups were divided into two subgroups on the basis of use or avoidance of estrogen replacement therapy (ERT). It was hypothesized that the high physical activity group would have greater BMC and BMD values than the low physical activity group. It was further hypothesized that the high physical activity group would have greater bone mineral values when the interaction of ERT was considered and when plasma estrogen (estrone and estradiol) levels were statistically controlled. The bone mineral measurements were obtained from the total body, lumbar spine (L1-L4), and proximal femur by dual energy radiography. Additional measures of physique, body composition, nutritional intake and plasma estrogen level were obtained. The high physical activity group did not have significantly greater bone mineral content or bone mineral density than the low physical activity group regardless of the skeletal site examined. When the interaction of physical activity and ERT use was examined, and when the plasma estrogen levels were statistically controlled, the women in the high physical activity group did not have significantly greater bone mineral density than the less active group. Additionally, there were no significantly different bone mineral values at any of the skeletal sites when the ERT users were compared to non-ERT users. Stepwise multiple regression analyses revealed that the fat-free body weight was the most significant independent variable contributor to the resultant BMC and BMD measurements of the subjects. The results indicate that high levels of physical activity, alone or in combination with ERT, were not associated with greater BMC and BMD measurements during the early postmenopausal years. The findings suggest that increased levels of physical activity may not provide adequate protection against the hormonally-related bone loss characteristic of the early menopausal years.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD
Work-a Journal of Prevention Assessment & Rehabilitation, Feb 13, 2023
BACKGROUND: Firefighting is a physiologically demanding occupation and there is a need to evaluat... more BACKGROUND: Firefighting is a physiologically demanding occupation and there is a need to evaluate physical and fitness characteristics that are related to attenuated physiological stress during fireground tasks. Previous studies have not measured associations between heart rate responses during simulated fireground tasks with a standardized work rate. OBJECTIVE: The purpose of this study was to examine associations between heart rate during a standardized pace simulated fireground test (SFGT) and heart rate recovery and variability following the SFGT. In addition, this study sought to evaluate associations between heart rate measures versus physical and fitness characteristics in structural firefighter recruits. METHODS: Twenty-one fire academy recruits performed a standardized pace SFGT while mean heart rate reserve (HRRes) during the SFGT, change in heart rate variability from rest to post-SFGT (LnRMSSDRest - Post), and 60-second post-SFGT heart rate recovery (HRR60) were measured. Regression analyses were conducted between HRRes, LnRMSSDRest - Post and HRR60 and between heart rate measures versus physical and fitness characteristics while accounting for differences in SFGT completion time. RESULTS: HRRes was associated with LnRMSSDRest - Post, but not HRR60. Height and pull-ups explained most of the variance in HRRes, height explained most of the variance in LnRMSSDRest - Post and push-ups and 1.5-mile run explained most of the variance in HRR60. CONCLUSION: Greater cardiovascular stress during fireground tasks is associated with greater depression of post-SFGT heart rate variability, but not heart rate recovery. Physical and fitness characteristics are important to consider in relation to firefighters’ ability to cope with physical stress on the fireground.
International Journal of Sports Physiology and Performance, Feb 1, 2018
Critical power (CP) and anaerobic work capacity (AWC) from the CP test represent distinct paramet... more Critical power (CP) and anaerobic work capacity (AWC) from the CP test represent distinct parameters related to metabolic characteristics of the whole body and active muscle tissue, respectively. This study examined the contribution of whole body composition characteristics and local lean mass to further elucidate the differences in metabolic characteristics between CP and AWC as they relate to whole body and local factors. Fifteen, anaerobically trained males were assessed for whole body (% body fat [%BF] and mineral-free, lean mass [LBM]) and local mineral-free thigh lean mass (TLM) composition characteristic. The CP and AWC were determined from the 3-min all-out CP test. Statistical analyses included Pearson product-moment correlations and stepwise multiple regression analyses (p ≤ 0.05). Only LBM contributed significantly to the prediction of CP (CP = 2.3[LBM] + 56.7 [r(2) = 0.346; SEE = 31.4W; p = 0.021]) and only TLM to AWC (AWC = 0.8[TLM] + 3.7 [r(2) = 0.479; SEE = 2.2kJ; p = 0.004]). These results indicated that the aerobic component (CP) of the CP test was most closely related to LBM and the anaerobic component (AWC), was more closely related to the TLM. These findings supported the theory that CP and AWC are separate measures of the whole body metabolic capabilities and the energy stores within the activated local muscle groups, respectively. Thus, training programs to improve CP and AWC should be designed to include resistance training exercises to increase whole body mineral-free lean mass and local mineral-free thigh lean mass.
Scandinavian Journal of Medicine & Science in Sports, Nov 28, 2022
BackgroundDiffusion tensor imaging (DTI) parameters correlate with muscle fiber composition, but ... more BackgroundDiffusion tensor imaging (DTI) parameters correlate with muscle fiber composition, but it is unclear how these relate to in vivo contractile function.PurposeTo determine the relationship between DTI parameters of the vastus lateralis (VL) and in vivo knee extensor contractile.MethodsThirteen healthy, premenopausal women underwent magnetic resonance imaging of the mid‐thigh to determine patellar tendon moment arm length and quadriceps cross‐sectional area. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) of the VL were determined using diffusion tensor imaging (DTI). Participants underwent an interpolated twitch (ITT) experiment before and after a fatiguing concentric‐eccentric isokinetic knee extension (60°·s−1). During the ITT, supramaximal electrical stimuli were delivered to elicit twitch responses from the knee extensors before, during, and after a maximal voluntary isometric contraction (MVIC). Knee extensor‐specific tension during twitch and MVIC were calculated from isometric torque data. Pearson's correlations were used to determine the relationship between muscle contractile properties and DTI parameters.ResultsMD and RD were moderately correlated with peak twitch force and rate of force development. FA and AD were moderately inversely related to percent change in MVIC following exercise.ConclusionMD and RD are associated with in vivo quadriceps twitch properties but not voluntary strength, which may reflect the mechanical properties of constituent fiber types. FA and AD appear to relate to MVIC strength following fatiguing exercise.
experimental autoimmune encephalomyelitis (EAE). Male Dark Agouti rats were induced with EAE and ... more experimental autoimmune encephalomyelitis (EAE). Male Dark Agouti rats were induced with EAE and 14 days later received subcutaneous (+)-NTX or saline for 14 days. Contextual-and auditory-fear conditioning were then conducted to assess memory impairments one week after beginning (+)-NTX administration. We found that EAE induced impairments in long-term contextual fear memory but not short-term contextual-or auditory-related fear memory. This effect was associated with increased interleukin-1b (IL-1bÞ mRNA expression in the hippocampus but not the amygdala. Importantly, (+)-NTX blocked EAE-induced impairments in longterm contextual fear memory and the associated increased hippocampal IL-1b expression. Moreover, (+)-NTX blocked hippocampal expression of TLR2, TLR4, NLRP3, and IL-17 mRNA, suggesting blockade of the TLR2/4, NLRP3 inflammasome and Th17 cell signaling as additional mechanisms by which (+)-NTX exerts its therapeutic effects. These findings support the role of TLR2/4 antagonists as potential treatments for MS-related cognitive deficits and encourage future research on TLR2/4 antagonists as treatments for various symptoms associated with inflammatory-related diseases, including MS.
Journal of science in sport and exercise, Jul 23, 2019
Purpose Critical resistance (CR) is a fatigue threshold that, theoretically, estimates the highes... more Purpose Critical resistance (CR) is a fatigue threshold that, theoretically, estimates the highest sustainable resistance for repeated skeletal muscle contractions. Men are typically more susceptible to fatigue than women during sustained muscular contractions. Therefore, the purpose of this study was to compare the CR between men and women to determine the sensitivity of the CR model to detect sex-related differences in fatigue at submaximal intensities. Methods Ten men and 10 women completed one-repetition maximum (1RM) testing for the deadlift and repetitions to failure at 50%, 60%, 70%, and 80% of 1RM for the determination of CR. Repetitions to failure were then performed at the estimated CR. The men had a greater absolute 1RM (168 ± 27 kg vs. 115 ± 11 kg) and CR (62 ± 14 kg vs. 48 ± 6 kg), but a lower relative CR (percent of 1RM; 37 ± 6% vs. 41 ± 2%) and completed fewer repetitions at CR (45 ± 14 repetitions vs. 58 ± 12 repetitions) compared to the women. Conclusions The CR model was sensitive to detect sex-related differences in fatiguing muscular contractions of the deadlift. In addition, the men were more susceptible to fatigue than the women during performance of submaximal muscular contractions at CR, which may be related to sex-dependent physiological responses during fatiguing muscular contractions.
Journal of Strength and Conditioning Research, 2019
Lesniak, AY, Bergstrom, HC, Clasey, JL, Stromberg, AJ, and Abel, MG. The effect of personal prote... more Lesniak, AY, Bergstrom, HC, Clasey, JL, Stromberg, AJ, and Abel, MG. The effect of personal protective equipment on firefighter occupational performance. J Strength Cond Res 34(8): 2165–2172, 2020—The purpose of this study was to evaluate the effects of load carriage (LC) and LC plus respirator use (LC + self-contained breathing apparatus [SCBA]) on firefighters' work capacity to enhance our understanding of occupational demands. Twenty-one male structural firefighter recruits (age: 28.6 ± 4.3 years; height: 178.6 ± 7.2 cm; body mass: 94.1 ± 15.4 kg; body fat: 22.9 ± 6.1%) participated. Occupational performance was assessed by time to complete a simulated fire ground test (SFGT). After 2 familiarization trials, recruits performed the following SFGT conditions in a randomized order: PT (physical training clothes), LC only, and LC + SCBA. To describe within-group differences between SFGT conditions, relative difference scores were calculated as follows: % difference = ([experiment...
Recommendations for endurance exercise prescription are often based on percentages of heart rate ... more Recommendations for endurance exercise prescription are often based on percentages of heart rate (HR) or the volume of oxygen consumption ( . VO 2 ) maximum or reserve that is extrapolated to a power output (P) or velocity. Previous work has demonstrated dissociations of the expected responses to exercise anchored to the critical heart rate (CHR) compared with the P associated with CHR. However, it is unclear if similar dissociations due to reductions in P to maintain the designated intensity would be present during exercise anchored to the . VO 2 associated with CHR ( . VO 2 CHR). The purpose of this study was to examine the patterns in physiological ( . VO 2 , HR, P, respiration rate [RR], muscle oxygen saturation [%SmO 2 ]), neuromuscular (electromyographic and mechanomyographic amplitude [EMG AMP, MMG AMP], mean power frequency [EMG MPF, MMG MPF]), and perceptual (rating of perceived exertion [RPE]) responses during exercise at . VO 2 CHR ( . VO 2 -clamp). On separate days, ten participants (age: 25 ± 4 yr) performed a graded exercise test and four constant P trials at 85-100% of peak P (PP) to derive CHR and . VO 2 CHR. Responses were recorded during a trial to exhaustion at . VO 2 CHR (32.86 ± 7.12 mL•kg -1 •min -1 ; T Lim = 31.31 ± 21.37 min) and normalized in 10% intervals of T Lim to their respective values at PP. The one-way repeated-measures ANOVA with post hoc, Bonferroni-corrected, pairwise comparisons indicated differences (p < 0.001) from baseline for HR (mean ± SD %change = 8 ± 3%), RR (43 ± 38%), P (-15 ± 5%), EMG MPF (10 ± 8%), and RPE (65 ± 38%), but no differences (p = 0.077-0.955) for %SmO 2 (-17 ± 53%), EMG AMP (-3 ± 16%), MMG AMP (40 ± 61%), and MMG MPF (1 ± 7%). The loss in performance observed during . VO 2 -Clamp exercise may provide a quantification of the inefficiency associated with the . VO 2 slow component phenomenon. The neuromuscular responses suggested constant muscle excitation despite the reductions in P, but the metabolic and perceptual responses suggested a combination of feedforward and feedback mechanisms regulating T Lim . Future studies should further examine responses to the . VO 2 -Clamp exercise at a uniform threshold.
The prevalence of hypertension is increasing particularly among obese children and adolescents. O... more The prevalence of hypertension is increasing particularly among obese children and adolescents. Obese children and adolescents with hypertension are likely to remain hypertensive as they reach adulthood and hypertension is linked to an increased risk for cardiovascular disease. Twenty-four-hour ambulatory blood pressure monitoring (ABPM) has become one of the most important tools in diagnosing hypertension in children and adolescents and circadian patterns of blood pressure may be important disease-risk predictors. Methods: A retrospective chart review was conducted in patients aged 6-21 years who underwent 24-h ABPM at Kentucky Children's Hospital (KCH) from August 2012 through June 2017. Exclusion criteria included conditions that could affect blood pressure including chronic kidney disease and other renal abnormalities, congenital heart disease, cancer, and thyroid disease. Subjects were categorized by body mass index into normal (below 85th percentile), overweight (85th-95th percentile), stage I obesity (95th-119th percentile), stage II obesity (120th-139th) and stage III obesity (>140th). Non-dipping was defined as a nocturnal BP reduction of <10%. Results: Two hundred and sixty-three patients (156 male patients) were included in the analysis, of whom 70 were normal weight, 33 overweight, 55 stage I obesity, 53 stage II, and 52 stage III obesity. Although there was no significant difference between normal weight and obese groups for prevalence of hypertension, there was a greater prevalence of SBP non-dipping in obese patients as BMI increased (p = 0.008). Furthermore, non-dippers had a significantly elevated LVMI as well as abnormal lab values for uric acid, blood lipid panel, creatinine, and TSH (p < 0.05). Conclusions: These findings demonstrate that obese children and adolescents constitute a large proportion of hypertensive children and adolescents and the severity of pediatric obesity is associated with nocturnal BP non-dipping. Additionally, obesity in children is linked to several cardiovascular risk factors including left ventricular hypertrophy, dyslipidemia, and elevated uric acid levels. Further studies utilizing ABPM measures on risk stratification in this very high-risk population are warranted.
Journal of Strength and Conditioning Research, Jul 1, 2019
Dinyer, TK, Byrd, MT, Garver, MJ, Rickard, AJ, Miller, WM, Burns, S, Clasey, JL, and Bergstrom, H... more Dinyer, TK, Byrd, MT, Garver, MJ, Rickard, AJ, Miller, WM, Burns, S, Clasey, JL, and Bergstrom, HC. Low-load vs. high-load resistance training to failure on one repetition maximum strength and body composition in untrained women. J Strength Cond Res 33(7): 1737-1744, 2019-This study examined the effects of resistance training (RT) to failure at low and high loads on one repetition maximum (1RM) strength and body composition (bone-and fat-free mass [BFFM] and percent body fat [%BF]) in untrained women. Twenty-three untrained women (age: 21.2 6 2.2 years; height: 167.1 6 5.7 cm; body mass: 62.3 6 16.2 kg) completed a 12-week RT to failure intervention at a low (30% 1RM) (n 5 11) or high (80% 1RM) (n 5 12) load. On weeks 1, 5, and 12, subjects completed 1RM testing for 4 different exercises (leg extension [LE], seated military press [SMP], leg curl [LC], and lat pull down [LPD]) and a dual-energy x-ray absorptiometry scan to assess body composition. During weeks 2-4 and 6-7, the subjects completed 2 sets to failure for each exercise. During weeks 8-11, the subjects completed 3 sets to failure for each exercise. The 1RM strength increased from week 1 to week 5 (LE:
261 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1993.The influence of high and ... more 261 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1993.The influence of high and low levels of physical activity on bone mineral content (BMC) and bone mineral density (BMD) was investigated in 60 healthy, Caucasian, early postmenopausal women. All women examined were a minimum of two but no more than five years past natural menstrual cessation. Subjects in the high physical activity group (n = 30) had an energy expenditure greater than 3000 kcal/week and in the low physical activity group (n = 30) less than 1500 kcal/week, estimated from walking, stair climbing, and sport and recreational activity participation. The physical activity groups were divided into two subgroups on the basis of use or avoidance of estrogen replacement therapy (ERT). It was hypothesized that the high physical activity group would have greater BMC and BMD values than the low physical activity group. It was further hypothesized that the high physical activity group would have greater bone mineral values when the interaction of ERT was considered and when plasma estrogen (estrone and estradiol) levels were statistically controlled. The bone mineral measurements were obtained from the total body, lumbar spine (L1-L4), and proximal femur by dual energy radiography. Additional measures of physique, body composition, nutritional intake and plasma estrogen level were obtained. The high physical activity group did not have significantly greater bone mineral content or bone mineral density than the low physical activity group regardless of the skeletal site examined. When the interaction of physical activity and ERT use was examined, and when the plasma estrogen levels were statistically controlled, the women in the high physical activity group did not have significantly greater bone mineral density than the less active group. Additionally, there were no significantly different bone mineral values at any of the skeletal sites when the ERT users were compared to non-ERT users. Stepwise multiple regression analyses revealed that the fat-free body weight was the most significant independent variable contributor to the resultant BMC and BMD measurements of the subjects. The results indicate that high levels of physical activity, alone or in combination with ERT, were not associated with greater BMC and BMD measurements during the early postmenopausal years. The findings suggest that increased levels of physical activity may not provide adequate protection against the hormonally-related bone loss characteristic of the early menopausal years.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD
Work-a Journal of Prevention Assessment & Rehabilitation, Feb 13, 2023
BACKGROUND: Firefighting is a physiologically demanding occupation and there is a need to evaluat... more BACKGROUND: Firefighting is a physiologically demanding occupation and there is a need to evaluate physical and fitness characteristics that are related to attenuated physiological stress during fireground tasks. Previous studies have not measured associations between heart rate responses during simulated fireground tasks with a standardized work rate. OBJECTIVE: The purpose of this study was to examine associations between heart rate during a standardized pace simulated fireground test (SFGT) and heart rate recovery and variability following the SFGT. In addition, this study sought to evaluate associations between heart rate measures versus physical and fitness characteristics in structural firefighter recruits. METHODS: Twenty-one fire academy recruits performed a standardized pace SFGT while mean heart rate reserve (HRRes) during the SFGT, change in heart rate variability from rest to post-SFGT (LnRMSSDRest - Post), and 60-second post-SFGT heart rate recovery (HRR60) were measured. Regression analyses were conducted between HRRes, LnRMSSDRest - Post and HRR60 and between heart rate measures versus physical and fitness characteristics while accounting for differences in SFGT completion time. RESULTS: HRRes was associated with LnRMSSDRest - Post, but not HRR60. Height and pull-ups explained most of the variance in HRRes, height explained most of the variance in LnRMSSDRest - Post and push-ups and 1.5-mile run explained most of the variance in HRR60. CONCLUSION: Greater cardiovascular stress during fireground tasks is associated with greater depression of post-SFGT heart rate variability, but not heart rate recovery. Physical and fitness characteristics are important to consider in relation to firefighters’ ability to cope with physical stress on the fireground.
International Journal of Sports Physiology and Performance, Feb 1, 2018
Critical power (CP) and anaerobic work capacity (AWC) from the CP test represent distinct paramet... more Critical power (CP) and anaerobic work capacity (AWC) from the CP test represent distinct parameters related to metabolic characteristics of the whole body and active muscle tissue, respectively. This study examined the contribution of whole body composition characteristics and local lean mass to further elucidate the differences in metabolic characteristics between CP and AWC as they relate to whole body and local factors. Fifteen, anaerobically trained males were assessed for whole body (% body fat [%BF] and mineral-free, lean mass [LBM]) and local mineral-free thigh lean mass (TLM) composition characteristic. The CP and AWC were determined from the 3-min all-out CP test. Statistical analyses included Pearson product-moment correlations and stepwise multiple regression analyses (p ≤ 0.05). Only LBM contributed significantly to the prediction of CP (CP = 2.3[LBM] + 56.7 [r(2) = 0.346; SEE = 31.4W; p = 0.021]) and only TLM to AWC (AWC = 0.8[TLM] + 3.7 [r(2) = 0.479; SEE = 2.2kJ; p = 0.004]). These results indicated that the aerobic component (CP) of the CP test was most closely related to LBM and the anaerobic component (AWC), was more closely related to the TLM. These findings supported the theory that CP and AWC are separate measures of the whole body metabolic capabilities and the energy stores within the activated local muscle groups, respectively. Thus, training programs to improve CP and AWC should be designed to include resistance training exercises to increase whole body mineral-free lean mass and local mineral-free thigh lean mass.
Scandinavian Journal of Medicine & Science in Sports, Nov 28, 2022
BackgroundDiffusion tensor imaging (DTI) parameters correlate with muscle fiber composition, but ... more BackgroundDiffusion tensor imaging (DTI) parameters correlate with muscle fiber composition, but it is unclear how these relate to in vivo contractile function.PurposeTo determine the relationship between DTI parameters of the vastus lateralis (VL) and in vivo knee extensor contractile.MethodsThirteen healthy, premenopausal women underwent magnetic resonance imaging of the mid‐thigh to determine patellar tendon moment arm length and quadriceps cross‐sectional area. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) of the VL were determined using diffusion tensor imaging (DTI). Participants underwent an interpolated twitch (ITT) experiment before and after a fatiguing concentric‐eccentric isokinetic knee extension (60°·s−1). During the ITT, supramaximal electrical stimuli were delivered to elicit twitch responses from the knee extensors before, during, and after a maximal voluntary isometric contraction (MVIC). Knee extensor‐specific tension during twitch and MVIC were calculated from isometric torque data. Pearson's correlations were used to determine the relationship between muscle contractile properties and DTI parameters.ResultsMD and RD were moderately correlated with peak twitch force and rate of force development. FA and AD were moderately inversely related to percent change in MVIC following exercise.ConclusionMD and RD are associated with in vivo quadriceps twitch properties but not voluntary strength, which may reflect the mechanical properties of constituent fiber types. FA and AD appear to relate to MVIC strength following fatiguing exercise.
experimental autoimmune encephalomyelitis (EAE). Male Dark Agouti rats were induced with EAE and ... more experimental autoimmune encephalomyelitis (EAE). Male Dark Agouti rats were induced with EAE and 14 days later received subcutaneous (+)-NTX or saline for 14 days. Contextual-and auditory-fear conditioning were then conducted to assess memory impairments one week after beginning (+)-NTX administration. We found that EAE induced impairments in long-term contextual fear memory but not short-term contextual-or auditory-related fear memory. This effect was associated with increased interleukin-1b (IL-1bÞ mRNA expression in the hippocampus but not the amygdala. Importantly, (+)-NTX blocked EAE-induced impairments in longterm contextual fear memory and the associated increased hippocampal IL-1b expression. Moreover, (+)-NTX blocked hippocampal expression of TLR2, TLR4, NLRP3, and IL-17 mRNA, suggesting blockade of the TLR2/4, NLRP3 inflammasome and Th17 cell signaling as additional mechanisms by which (+)-NTX exerts its therapeutic effects. These findings support the role of TLR2/4 antagonists as potential treatments for MS-related cognitive deficits and encourage future research on TLR2/4 antagonists as treatments for various symptoms associated with inflammatory-related diseases, including MS.
Journal of science in sport and exercise, Jul 23, 2019
Purpose Critical resistance (CR) is a fatigue threshold that, theoretically, estimates the highes... more Purpose Critical resistance (CR) is a fatigue threshold that, theoretically, estimates the highest sustainable resistance for repeated skeletal muscle contractions. Men are typically more susceptible to fatigue than women during sustained muscular contractions. Therefore, the purpose of this study was to compare the CR between men and women to determine the sensitivity of the CR model to detect sex-related differences in fatigue at submaximal intensities. Methods Ten men and 10 women completed one-repetition maximum (1RM) testing for the deadlift and repetitions to failure at 50%, 60%, 70%, and 80% of 1RM for the determination of CR. Repetitions to failure were then performed at the estimated CR. The men had a greater absolute 1RM (168 ± 27 kg vs. 115 ± 11 kg) and CR (62 ± 14 kg vs. 48 ± 6 kg), but a lower relative CR (percent of 1RM; 37 ± 6% vs. 41 ± 2%) and completed fewer repetitions at CR (45 ± 14 repetitions vs. 58 ± 12 repetitions) compared to the women. Conclusions The CR model was sensitive to detect sex-related differences in fatiguing muscular contractions of the deadlift. In addition, the men were more susceptible to fatigue than the women during performance of submaximal muscular contractions at CR, which may be related to sex-dependent physiological responses during fatiguing muscular contractions.
Journal of Strength and Conditioning Research, 2019
Lesniak, AY, Bergstrom, HC, Clasey, JL, Stromberg, AJ, and Abel, MG. The effect of personal prote... more Lesniak, AY, Bergstrom, HC, Clasey, JL, Stromberg, AJ, and Abel, MG. The effect of personal protective equipment on firefighter occupational performance. J Strength Cond Res 34(8): 2165–2172, 2020—The purpose of this study was to evaluate the effects of load carriage (LC) and LC plus respirator use (LC + self-contained breathing apparatus [SCBA]) on firefighters' work capacity to enhance our understanding of occupational demands. Twenty-one male structural firefighter recruits (age: 28.6 ± 4.3 years; height: 178.6 ± 7.2 cm; body mass: 94.1 ± 15.4 kg; body fat: 22.9 ± 6.1%) participated. Occupational performance was assessed by time to complete a simulated fire ground test (SFGT). After 2 familiarization trials, recruits performed the following SFGT conditions in a randomized order: PT (physical training clothes), LC only, and LC + SCBA. To describe within-group differences between SFGT conditions, relative difference scores were calculated as follows: % difference = ([experiment...
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