Biomedical subjects

John K Petrella

Publications and source records attributed to John K Petrella.

8 recordsLinked to original sources

PubMed2006

Contributions of force and velocity to improved power with progressive resistance training in young and older adults.

We investigated the effects of age on changes in the force and velocity components of knee extension (KE) power during 16 weeks of traditional progressive resistance training (PRT). Thirty-one young (27 +/- 1 years, 16 men, 15 women) and 30 older (64 +/- 1 years, 14 men, 16 women) adults trained by KE, leg press, and squat 3 days/week. PRT consisted of three sets with an appropriate load for 8-12 repetitions to fatigue. Testing occurred at baseline, 8, and 16 weeks. Thigh lean mass (TLM) was measured by DEXA. KE load-power and load-velocity curves were generated from peak concentric contractions against loads equivalent to 20, 30, 40, 50, and 60% maximum voluntary isometric contraction (MVC) force. Quadriceps neural activation relative to maximum was assessed during a sit-to-stand task. Participants increased KE 1RM (P < 0.05) by 8 weeks with young adults also increasing strength from 8 to 16 weeks. Adjusting for TLM, all groups increased KE specific strength (P < 0.05). MVC improved by 8 weeks in older adults and by 16 weeks in young subjects (P < 0.05). Neural activation requirements during standing and sitting declined in older adults by 8 weeks (P < 0.05). The KE load-power curve improved for all groups (P < 0.05) by 8 weeks with only young adults improving from 8 to 16 weeks. Peak concentric velocity increased only in older adults (P < 0.05). Training improvements in power resulted primarily from increases in strength both early and late for young adults while older adults realized early improvements in both strength and peak concentric velocity.

Adaptation, Physiological↗

PubMed2006

Efficacy of myonuclear addition may explain differential myofiber growth among resistance-trained young and older men and women.

Skeletal muscle stem (satellite) cells supporting growth/regeneration are thought to be activated and incorporated into growing myofibers by both endocrine and locally expressed autocrine/paracrine growth factors, the latter being load sensitive. We recently found that myofiber hypertrophy with resistance training is superior in young men (YM) vs. young women and older adults (Kosek DJ, Kim JS, Petrella JK, Cross JM, and Bamman MM. J Appl Physiol 101: 531-544, 2006). We hypothesized that the advanced myofiber hypertrophy in YM is facilitated by myonuclear addition in response to a milieu promoting stem cell activation. Twenty-six young (27.0 +/- 1 yr, 50% women) and 26 older (63.7 +/- 1 yr, 50% women) adults completed 16 wk of knee extensor resistance training. Vastus lateralis biopsies were obtained at baseline, 24 h after one bout, and after 16 wk. Muscle stem cells were identified immunohistochemically with anti-neural cell adhesion molecule (NCAM+). Muscle transcript levels of IGF-I and mechanogrowth factor (MGF) were determined by RT-PCR. Serum IGF-I, IGF-binding protein (IGFBP)-3, IGFBP-1, total and free testosterone, sex hormone-binding globulin (SHBG), and androstenedione were assessed by radioimmunoassay. Myofiber hypertrophy was twofold greater in YM vs. others, and only YM increased NCAM+ cells per 100 myofibers (49%) and myonuclei per fiber (19%) (P < 0.05). IGF-IEa mRNA was higher in young and increased acutely (29%) with summation by 16 wk (96%) (P < 0.05). MGF mRNA increased only in young after one bout (81%) and by 16 wk (85%) (P < 0.001). Circulating IGF-I was twofold higher in young, whereas IGFBP-1 was lowest in YM (P < 0.05). Among men, free testosterone was 59% higher in YM (P < 0.01). Myonuclear addition was most effectively accomplished in YM, which likely drove the superior growth.

Adult↗

PubMed2006

Efficacy of 3 days/wk resistance training on myofiber hypertrophy and myogenic mechanisms in young vs. older adults.

Resistance training (RT) has shown the most promise in reducing/reversing effects of sarcopenia, although the optimum regime specific for older adults remains unclear. We hypothesized myofiber hypertrophy resulting from frequent (3 days/wk, 16 wk) RT would be impaired in older (O; 60-75 yr; 12 women, 13 men), sarcopenic adults compared with young (Y; 20-35 yr; 11 women, 13 men) due to slowed repair/regeneration processes. Myofiber-type distribution and cross-sectional area (CSA) were determined at 0 and 16 wk. Transcript and protein levels of myogenic regulatory factors (MRFs) were assessed as markers of regeneration at 0 and 24 h postexercise, and after 16 wk. Only Y increased type I CSA 18% (P < 0.001). O showed smaller type IIa (-16%) and type IIx (-24%) myofibers before training (P < 0.05), with differences most notable in women. Both age groups increased type IIa (O, 16%; Y, 25%) and mean type II (O, 23%; Y, 32%) size (P < 0.05). Growth was generally most favorable in young men. Percent change scores on fiber size revealed an age x gender interaction for type I fibers (P < 0.05) as growth among Y (25%) exceeded that of O (4%) men. Myogenin and myogenic differentiation factor D (MyoD) mRNAs increased (P < 0.05) in Y and O, whereas myogenic factor (myf)-5 mRNA increased in Y only (P < 0.05). Myf-6 protein increased (P < 0.05) in both Y and O. The results generally support our hypothesis as 3 days/wk training led to more robust hypertrophy in Y vs. O, particularly among men. However, this differential hypertrophy adaptation was not explained by age variation in MRF expression.

Adult↗

PubMed2005

Resting and load-induced levels of myogenic gene transcripts differ between older adults with demonstrable sarcopenia and young men and women.

Regenerative capacity appears to be impaired in sarcopenic muscle. As local growth factors and myogenic regulatory factors (MRFs) modulate repair/regeneration responses after overload, we hypothesized that resistance loading (RL)-induced expression of MRFs and muscle IGF-I-related genes would be blunted in older (O) males (M) and females (F) with demonstrable sarcopenia vs. young (Y) adults. Y (20-35 yr, 10 YF, 10 YM) and O (60-75 yr, 9 OF, 9 OM) underwent vastus lateralis biopsy before and 24 h after knee extensor RL. Sarcopenia was assessed by cross-sectional area of type I, IIa, and IIx myofibers. Transcript levels were assessed by relative RT-PCR and analyzed by age x gender x load repeated-measures ANOVA. O were sarcopenic based on type II atrophy with smaller type IIa (P < 0.05) and IIx (P < 0.001) myofibers. Within-gender cross-sectional area differences were more marked in F (OF < YF: IIa 21%, IIx 42%). Load effects (P < 0.05) were seen for four of seven mRNAs as IGF-IEa (34%), myogenin (53%), and MyoD (20%) increased, and myf-6 declined 10%. Increased IGF-IEa was driven by O (48%) and/or M (43%). An age x gender x load interaction was found for MyoD (P < 0.05). An age x load interaction for type 1 IGF receptor (P < 0.05) was driven by a small increase in O (16%, P < 0.05). A gender x load interaction (P < 0.05) was noted for IGF binding protein-4. Age effects (P < 0.05) resulted from higher MyoD (54%), myf-5 (21%), and IGF binding protein-4 (17%) in O and were primarily localized to F at baseline (OF > YF; MyoD 94%, myf-5 47%, P < 0.05). We conclude that RL acutely increases mRNA expression of IGF-IEa and myogenin, which may promote growth/regeneration in both Y and O. Higher resting levels of MRFs in OF vs. YF suggest elevated basal regenerative activity in sarcopenic muscle of OF.

Adult↗

PubMed2005

Continuous-scale physical functional performance test: validity, reliability, and sensitivity of data for the short version.

BACKGROUND AND PURPOSE: The Continuous-Scale Physical Functional Performance Test (CS-PFP) can be used to obtain valid, reliable, and sensitive measurements of physical functional capacity. This test requires a fixed laboratory space and approximately 1 hour to administer. This study was carried out in 4 steps, or substudies, to develop and validate a short, community-based version (PFP-10) that requires less space and equipment than the CS-PFP. SUBJECTS AND METHODS: Retrospective data (n=228) and prospective data (n=91) on men and women performing the CS-PFP or the PFP-10 are reported. A 12-week exercise program was used to examine sensitivity to change. Data analyses were done using paired t-test, Pearson correlation, intraclass correlation coefficient (ICC), and delta index (DI) procedures. RESULTS: The PFP-10 total score and 4 of the 5 domain scores were statistically similar (within 3%) to those of the CS-PFP. The PFP-10 upper-body strength domain score was 17% lower, but was highly correlated (ICC=.97). Community and established laboratory PFP-10 scores were similar (ICC=.85-.97). The PFP-10 also is sensitive to change (DI=.21-.54). DISCUSSION AND CONCLUSION: The PFP-10 yields valid, reliable, and sensitive measurements and can be confidently substituted for the CS-PFP.

Activities of Daily Living↗

PubMed2004

Age differences in knee extension power, contractile velocity, and fatigability.

The purposes of this study were to examine age and gender differences in knee extensor strength, power, and fatigue using open- and closed-chain testing procedures. We tested the hypothesis that specific strength (strength/unit muscle mass) would not differ by age, whereas age differences in specific power and fatigue would remain consequent to blunted maximal contractile velocity. Skeletal muscle performance was examined in 28 young (26.9 +/- 0.7 yr) and 24 older (63.6 +/- 0.8 yr) men and women. Assessments included one-repetition maximum strength for knee extension, leg press, and squat; concentric knee extensor peak power, velocity, and fatigability; and sit-to-stand power, fatigability, and relative neural activation (electromyograph activity during sit-to-stand movement normalized to electromyograph activity during isometric maximum voluntary contraction). Thigh lean mass (TLM; kg) was assessed by dual-energy X-ray absorptiometry. Specific strength (N/kg TLM) and specific power (W/kg TLM) were estimated by dividing absolute values by TLM. Age differences in specific strength were observed for knee extension only (young, 41.2 +/- 1.0 N/kg TLM; older, 32.4 +/- 1.0 N/kg TLM; P < 0.05). Adjustment for TLM did not negate age differences in knee extension specific power (25-41% lower in older; P < 0.05) across loads tested. Older adults experienced fatigue across 10 repetitions of knee extension as peak velocity fell by 24% (P < 0.05). Deficits in concentric power persist after adjustment for TLM as maximum contractile velocity falls markedly with aging. Older adults are less capable of sustaining maximum concentric velocity during repetitive contractions. These findings suggest that velocity impairments are a possible contributor to mobility loss and falls risk among older adults. Interventions for improving contractile velocity should be pursued.

Adult↗

PubMed2004

Leg extensor power, cognition, and functional performance in independent and marginally dependent older adults.

BACKGROUND: physical and cognitive function must be integrated and optimised in performance of daily activities. Age-related loss of physical function can result in poor performance of necessary daily activities and possibly lead to increased dependency and a change of living status. OBJECTIVES: (1) to evaluate average differences in physiological, cognitive, and functional performance of older adults from two different levels of independence, (2) to examine contributions of leg power, cognition, and functional performance to level of independence. DESIGN: cross-sectional study of self-reported 'independent' versus 'marginally dependent' older adults. SUBJECTS: 35 older adults (77.2 +/- 6 years) were placed into independent (n = 18) or marginally dependent (n = 17) groups based upon the Medical Outcomes Study SF36 physical function scores (independent: SF36PF > or = 85, marginally dependent: SF36PF < 85) and living status. METHODS: assessment of physical function includes the dependent variable, SF36PF. Assessment of physical, cognitive, and functional performance include the independent variables of leg extensor power, reaction time, processing speed, memory, attention, and functional performance. Functional performance is assessed by the Continuous Scale Physical Functional Performance Test. RESULTS: independent older adults have greater performance on leg power, reaction time, processing speed, memory, and functional performance than marginally dependent older adults. Functional performance is an independent predictor of level of independence. Leg power and cognition were separate small but significant predictors of independence. CONCLUSIONS: independent older adults have greater physiological, cognitive and functional performance than marginally dependent older adults. Individuals with greater functional performance tend to remain independent.

Activities of Daily Living↗

PubMed2004

Daily ambulation activity and task performance in community-dwelling older adults aged 63-71 years with preclinical disability.

BACKGROUND: The purpose of this study was to examine differences in daily ambulation activity and task modification between community-dwelling older adults above and below an empirically derived physical threshold that has been linked to independence. METHODS: 20 community-dwelling older adults (72.8 +/- 6 years) were categorized into groups based on functional performance using the Continuous scale Physical Functional Performance Test total score (Cs-PFP). Individuals with Cs-PFP > or =57 were assigned to the high functioning group (HIGH; n=10) with all others assigned to the lower functioning group (LOW; Cs-PFP<57; n=10). Dependent variables included steps/day, number of tasks reported with difficulty, and number of tasks reported with modification. RESULTS: HIGH took significantly more steps/day (HIGH: 9503 +/- 4623; LOW: 5048 +/- 2917, p=.019) compared to LOW. Groups reported having difficulty with a similar number of tasks (HIGH: 0.4 +/- 1; LOW: 1.0 +/- 1, p=.092) but LOW reported modifying a significantly larger number of tasks (HIGH: 0.3 +/- 1; LOW 1.4 +/- 1, p=.049). CONCLUSIONS: Older adults with preclinical disability have reduced daily ambulatory activity compared to older adults with high function despite a similar independent living status. Individuals compensate for reduced physical reserves by modifying the method of performing a task. Identifying early declines in physical ability through task modification and daily ambulation will provide the opportunity for timely intervention to older adults desiring to remain independent within a community-dwelling environment.

Activities of Daily Living↗