The Effect of Static Stretching and Order of Warm-Up on the Isokinetic Peak Torque of the Knee Extensors

The purposes of these studies were to determine if an acute static stretch influenced isokinetic peak torque (IPT), and to examine if the order in which the warm up routine was performed affected peak knee extension torque. Twenty trained college male students performed maximal isokinetic knee extensions under four conditions: a control consisting of no stretching, a stretch only trial, jog then stretch, and stretch then jog conditions. Each stretch was held for a total volume of 360 s. Measurements were taken on a Biodex System 3 isokinetic dynamometer at speeds of 60º s-1 and 300º s-1. Data were analyzed using t-tests to compare the stretch condition with the control. The results indicated that there was a significant difference between the stretch and the control at 300 º s-1 (p = 0.03 t = 2.42) but not at 60 º s-1 (p = 0.16). A 2 x 3 ANOVA (300 º s-1 x 60 º s-1, and control x stretch then jog x jog then stretch) yielded no significance at either speed (p \u3e 0.05). Conclusions from this study indicate that stretching should not be the sole exercise in a warm-up routine as previous research confirms the decrease in IPT after stretching. Another finding of this study is that the negative effects of stretching can be diminished when combined with an aerobic activity such as jogging prior to performance. Further research is needed to determine the underlying factors that contribute to the post stretch decrease in IPT and the factors that lead to the restoration of force after aerobic activity. Caution is advised since these were controlled tests in a laboratory and results may vary with actual performance

Age-Related Differences in Vertical Jump Power and Muscle Size and Quality of the Vastus Lateralis

Previous studies have reported that decreases in muscle size and quality of the vastus lateralis (VL) may contribute to the lower vertical jump power observed in old compared to young males. However, we are aware of no previous studies that have examined the contribution of VL muscle size and quality to age-related power differences in females, nor have there been any studies that examined these differences between young, middle, and older age groups. PURPOSE: To determine the effects of age on vertical jump power and muscle size (cross-sectional area [CSA]) and quality (echo intensity [EI]) of the VL in young, middle-aged, and old females. METHODS: Twenty-six young (age = 22 ± 2 yr; height = 163 ± 7 cm; mass = 61 ± 8 kg), 30 middle-aged (36 ± 5 yr; 164 ± 7 cm; 62 ± 11 kg), and 23 old (71 ± 5 yr; 161 ± 5 cm; 59 ± 10 kg) females underwent two diagnostic ultrasound assessments followed by three countermovement vertical jumps (CMJs). Peak power output (Pmax; W) was measured during the CMJs using a portable force plate. VL CSA (cm2) and EI (AU) were measured on the right leg using a portable B-mode ultrasound imaging device and linear-array probe. One-way ANOVAs and post-hoc analyses were used to compare Pmax, CSA, and EI between age groups. Pearson product-moment correlation coefficients (r) were used to examine the relationships between Pmax and CSA and EI. RESULTS: Higher Pmax and CSA values were observed for the young (Pmax = 2257.40 ± 438.42 W; CSA = 20.59 ± 4.23 cm2) compared to the old (Pmax = 1098.55 ± 242.10 W; CSA = 10.69 ± 2.47 cm2) and middle-aged (Pmax = 1958.20 ± 341.87 W; CSA = 18.05 ± 4.24 cm2) and the middle-aged compared to the old (P ≤ 0.001-0.039). EI values for the young (104.29 ± 16.86 AU) and middle-aged (107.71 ± 17.30 AU) were lower than the old (128.35 ± 14.99 AU) (P \u3c 0.001), but they were not different from each other (P = 0.720). There was a significant positive relationship between Pmax and CSA (r = 0.830; P \u3c 0.001) and a significant negative relationship between Pmax and EI (r = -0.442; P \u3c 0.001). CONCLUSION: These findings demonstrated that vertical jump power and muscle size and quality decrease with age. The significant relationships observed between Pmax and CSA and EI perhaps suggest that these age-related declines in VL muscle size and quality may play an important role in the lower vertical jump power observed in middle-aged and older adults

Dietary protein intake is associated with maximal and explosive strength of the leg flexors in young and older blue collar workers

The aim of this study was to investigate the association between dietary PRO intake and maximal and rapid strength of the leg flexors in blue collar (BC) working men. Twenty-four young (age=23.2±2.1 yrs), and nineteen older aged (age=52.8±5.2 yrs) men employed in BC occupations completed a three day dietary record and isometric strength testing of the leg flexors. Food logs were analyzed for total protein (TPRO) and essential amino acid (EAA) intake. Rapid and maximal strength capacities were examined from the rate of torque development at 50ms (RTD50) and peak torque (PT) of the torque-time curves, respectively. Pearson correlations and partial correlations were used to examine the relationships between TPRO and EAA intake on strength variables. PT was positively correlated to TPRO and EAA intake in the young (r=0.439 and 0.431;P0.05) between TPRO and strength variables when controlling for EAA intake. TPRO intake explained 20–44% of the variance in rapid and maximal strength for both age groups. EAA intake was largely responsible for the positive relationship between PRO intake and strength. Across young and older aged blue collar working male populations, protein consumption was associated with both maximal and explosive strength capacities of the leg flexors muscle group

The Relationships between Internal and External Load Measures for Division I College Football Practice

The aim of this study is to explore the relationships between internal and external load measures in American football. Thirty football players wore a portable integrated monitor unit for 10 weeks during the fall football season. Relationships between internal and external load measurements were determined. Internal load consisted of heart rate zones and heart rate-derived measures and session Ratings of Perceived Exertion (sRPE). External load consisted of distance in different speed zones, total distance traveled, and accelerations. There were many significant positive relationships, but the meaningful relationships (r > 0.5) were between heart rate-derived measures of load (Training Impulse and heart rate reserve) and low-intensity movement and total distance. Only accelerations between 1 and 1.99 m·s−2 were moderately correlated to heart rate-derived internal load. RPE values alone did not correlate strong enough with any of the measure but sRPE training load (sRPE-TL) correlated to most external values. Overall, moderate correlations were present between heart rate-derived internal load to total distance and lower intensity movement. sRPE-TL values had high correlations but were highly dependent on duration, not perceived exertion. When addressing load in American football, duration of the session is a key component in determining internal load as HR data and sRPE alone do not correlate highly with external loads

Comparison of Age-Specific Leg Extensor Muscle Function Torque-Time and Rapid Velocity Attributes Across the Adult Lifespan: A Relative Deficiency Investigation

The purposes of this study were to examine the age-related differences in absolute and normalized torque-time parameters in five distinct groups across the adult lifespan, and the relationship between rapid strength and limb acceleration capacities across the lifespan. One-hundred and thirty-six healthy men were categorized as young athletes (n = 27; age = 20.7 yrs), young controls (n = 32; 21.9 yrs), middle young (n = 32; 49.8 yrs), middle old (n = 15; 58.9 yrs), and old (n = 30; 71.3 yrs) cohorts. Participants performed maximal voluntary contractions (MVCs) of the leg extensors under isometric and isokinetic (240 deg.·s−1) conditions. Outcome measures included peak torque (PT), absolute and MVC normalized (norm) rate of torque development (RTD) at 50 and 200 ms, RTD50/PT ratio, and rate of velocity development (RVD). The PT and absolute RTD at 200 ms declined from young to old age (P \u3c .05). The middle age groups exhibited an overall preservation of early RTD, and a potential enhancement of early normalized RTD (P = .06 for middle young vs. controls, for RTDnorm50). The RTD50/PT ratio was higher in the middle young (P \u3c .05) compared to both the young groups. Generally, the RVD declined more linearly and exhibited worse preservation at mid-life than the early absolute or normalized RTD variables. All absolute torque-time variables were correlated (r = 0.43–0.73, P \u3c .001) to the RVD for all groups combined. These findings showed distinct age-related declines occurred for different muscle function parameters unique to specific stages of the lifespan. Normalized RTD variables may reveal plausible mechanisms of age-related neuromuscular changes and the RTD50/PT ratio may be a useful tool for determining relative deficiencies, such that mid-life adults (45–64 yrs) should address their relative limitation of PT by enhancing strength at mid-life, whereas older adults (65+ yrs) may need more emphasis on RTD improvements. In addition, both mid-life and older men should seek to improve rapid limb velocity capacities due to the susceptibility of RVD to decline more incrementally across the lifespan. Such information may help to improve anti-aging strategies by countering age-specific muscle function deficiencies and may improve mid-life adults\u27 ability to transition better functionally into old age

The influence of occupation and age on maximal and rapid lower extremity strength

The aims of this study were to 1) examine the influence of age and occupation on maximal and rapid strength of the lower-extremity muscles and 2) examine the relationship between maximal and rapid strength and physical workload (work index (WI)) in the blue-collar (BC) cohort. Peak torque (PT) and peak rate of torque development (peakRTD) of the leg extensors (LE), leg flexors (LF), and plantar flexors (PF) were assessed in 47 young (age = 24.1 ± 2.4 years) and 41 middle-aged (52.4 ± 5.2 years) white-collar (WC) and BC men. Middle-aged workers exhibited lower PT for all muscles, and peakRTD for the LF and PF muscles. A positive relationship (r = 0.59; P \u3c 0.01) was observed between WI and peakRTD for the PF in the young BC workers, however, this relationship was negative (r = −0.45; P = 0.053) for the LF of the middle-aged BC workers. Lowering physical work demands and/or incorporating effective health-related practices for employees may be appealing strategies to enhance aging workers\u27 productivity and longevity in the workforce

The influence of manual labor at work on muscular fitness and its relationship with work performance

Objective: The present study examined the influence of workplace manual labor on measures of muscular fitness, with a secondary aim to investigate the relationship between muscular fitness and work performance in blue-collar (BC) workers. Methods: Leg extension isokinetic strength at slow and fast velocities, hamstring and hip-flexor flexibility, and low back muscular endurance were examined in young and older BC workers and white-collar (WC) controls, while work performance was examined in the BC cohort. Results: There were no differences in muscular fitness variables between BC and WC groups; however, the older men had lower low back muscular endurance (−43.0%) and strength at slow (−9.4%) and fast (−12.7%) velocities. Work performance was associated with strength at fast velocities (r = 0.633) in the older BC workers. Conclusions: Leg strength may influence work performance, with higher velocities becoming more important in older workers