Lori L. Ploutz-Snyder

Orientation and Familiarization to 1RM Strength Testing in Old and Young Women.

The purpose of this study was to compare the number of testing sessions required to achieve consistent 1 repetition maximum (1RM) strength measurements in untrained old and young women. Consistency of measurement was defined as consecutive 1 RM strength measures that increased by 1 kg or less. Untrained old (n = 6, age 66 ± 5 years) and untrained young (n = 7, age 23 ± 4 years) women were repeatedly strength-tested for bilateral concentric knee extension 1 RM strength until consecutive measurements were increased by no more than 1 kg. At least 48 hours of rest was allowed between 1 RM measurements. The old subjects required significantly more testing sessions (8–9 sessions) compared with the young subjects (3–4 sessions) to achieve the same absolute consistency of measurement (p < 0.05). Absolute increase in strength between the first and final testing sessions did not differ between groups (young = 11 ± 4 kg and old = 13 ± 2 kg) (p > 0.05). The relative increase was significantly greater in the older subjects (young = 12 ± 5%; old = 22 ± 4%) (p < 0.05). In conclusion, older subjects require more practice and familiarization and show greater relative increases in 1RM strength when compared with younger subjects of the same experience level. This is important to consider, especially when evaluating the magnitude of strength increase in response to esistance training.

Benefits for bone from resistance exercise and nutrition in long-duration spaceflight: Evidence from biochemistry and densitometry

Exercise has shown little success in mitigating bone loss from long‐duration spaceflight. The first crews of the International Space Station (ISS) used the “interim resistive exercise device” (iRED), which allowed loads of up to 297 lbf (or 1337 N) but provided little protection of bone or no greater protection than aerobic exercise. In 2008, the Advanced Resistive Exercise Device (ARED), which allowed absolute loads of up to 600 lbf (1675 N), was launched to the ISS. We report dietary intake, bone densitometry, and biochemical markers in 13 crewmembers on ISS missions from 2006 to 2009. Of these 13, 8 had access to the iRED and 5 had access to the ARED. In both groups, bone‐specific alkaline phosphatase tended to increase during flight toward the end of the mission (p = 0.06) and increased 30 days after landing (p < 0.001). Most markers of bone resorption were also increased in both groups during flight and 30 days after landing (p < 0.05). Bone densitometry revealed significant interactions (time and exercise device) for pelvis bone mineral density (BMD) and bone mineral content (p < 0.01), hip femoral neck BMD (p < 0.05), trochanter BMD (p < 0.05), and total hip BMD (p < 0.05). These variables were unchanged from preflight only for ARED crewmembers, who also returned from flight with higher percent lean mass and lower percent fat mass. Body mass was unchanged after flight in both groups. All crewmembers had nominal vitamin D status (75 ± 17 nmol/L) before and during flight. These data document that resistance exercise, coupled with adequate energy intake (shown by maintenance of body mass determined by dual‐energy X‐ray absorptiometry [DXA]) and vitamin D, can maintain bone in most regions during 4‐ to 6‐month missions in microgravity. This is the first evidence that improving nutrition and resistance exercise during spaceflight can attenuate the expected BMD deficits previously observed after prolonged missions.

Physical fitness predicts functional tasks in individuals with Down syndrome.

UNLABELLED Individuals with Down syndrome (DS) exhibit reduced strength and aerobic capacity, which may limit their ability to perform functional tasks of daily living. PURPOSE This study was conducted to examine the relationship between timed performance on functional tasks of daily living and age, knee isometric strength, and peak aerobic capacity in a group of individuals with DS. METHODS This was a cross-sectional study involving 35 individuals (27 +/- 7.5 yr) with DS. Participants completed an isometric test of knee extensor and flexor strength, an individualized exercise test to measure peak aerobic capacity, and three timed functional tasks of daily living, which included chair rise, gait speed, and stair ascent and descent. Multiple regression analyses were performed to examine the relationship between timed task performance and age, knee isometric strength, and peak aerobic capacity. RESULTS The multiple regression models explained 11-29% of the variance in timed task performance. Knee extensor strength was the most influential variable in predicting timed task performance (squared semipartial correlation coefficient [sr2] = 0.11-0.20), followed by aerobic capacity (sr2 = 0.10-0.14). Age was not a significant predictor of timed task performance. CONCLUSION These findings suggest that physical fitness (defined here as aerobic capacity and knee extensor strength) limits the ability of adults with DS to perform functional tasks of daily living. Randomized controlled trials should be performed to test the probable causal relationship between exercises designed to improve physical fitness and functional tasks of daily living.

Skeletal muscle glycogen loss evoked by resistance exercise

Biopsies were taken from the left m. vastus lateralis of 9 young men and analyzed for mixed muscle and for single fiber glycogen to infer recruitment, especially among fast-twitch subtypes, during knee extensions with loads of 30, 45, and 60% of 1-repetition maximum. The relative decline in mixed muscle glycogen was related to relative exercise load, as were the percentage of fast-twitch fibers showing glycogen loss and the relative cross-sectional area (CSA) of m. vastus lateralis occupied by type Ha or by fast-twitch fibers that showed glycogen loss (p ≤ 0.0478, r ≥ 0.50). The relative decline in mixed m. vastus lateralis glycogen was related to the percentage of both fast-twitch fibers and type Ha fibers, and the relative CSA of m. vastus lateralis occupied by type IIa fibers that showed glycogen loss (p ≤ 0.0436, r ≥ 0.51). Type I and IIa fibers were used for all 3 bouts. Type IIab + IIb fibers showed glycogen loss for the heaviest load. The results suggest that mixed muscle glycogen loss is related to load, mainly due to fast fiber usage. It also appears that the general understanding put forth for cycling and running—that fast-twitch fiber type use depends on exercise intensity—holds for resistance exercise. Because type IIab + IIb fibers showed glycogen loss at loads of 60% of maximum, it is suggested that fast-twitch subtypes are used at lower loads than generally appreciated.

Relationship between muscle T2* relaxation properties and metabolic state: a combined localized 31P-spectroscopy and 1H-imaging study

Abstract A multi-volume 31P-magnetic resonance spectroscopy localization procedure was implemented to compare directly muscle metabolism and proton T2* relaxation properties in the human plantar flexor muscles during exercise. Localized 31P-spectra were collected simultaneously from the medial gastrocnemius, lateral gastrocnemius and soleus muscles during exercise using β1-insensitive Hadamard Spectroscopic Imaging (HSI). 1H T2*-weighted gradient-echo images were acquired at rest and immediately following high-intensity plantar flexion exercise. T2* mapping of the individual calf muscles showed that plantar flexion with the knee extended produces significant increases (P < 0.0001) in the mean (SEM) T2* of the medial [35.6 (1.2) ms vs 28.5 (0.5) ms at rest] and lateral gastrocnemius [35.6 (0.9) ms vs 26.2 (0.9) ms at rest], but not in the soleus [26.7 (0.6) ms vs 27.3 (0.8) ms at rest]. In accordance with the changes in T2*, the ratio of inorganic phosphate to phosphocreatine (Pi:PCr) and the intracellular muscle pH shifted significantly in the gastrocnemii, while the soleus showed no change in muscle pH and only a moderate increase in Pi-to-Ph. Comparison of spectroscopic and relaxation parameters in both gastrocnemius muscles revealed a significant relationship between post-exercise T2* and intracellular pH (r=0.72–0.76) and Pi-to-Ph ratios (r=0.81–0.88) during exercise. Using an improved method of localization, this study confirms the existence of a strong relationship between transverse relaxation properties and the metabolic state in skeletal muscles engaged in heavy exercise.

Derecruitment of the lumbar musculature with fatiguing trunk extension exercise.

Study Design. This was a descriptive study involving 20 healthy individuals. Objectives. To evaluate the neuromuscular activation patterns of the lumbar paraspinal and hip extensor muscles during isotonic trunk extension exercise. Summary of Background Data. Few studies have evaluated the effect of muscle fatigue on the lumbar musculature during isotonic exercise. Methods. Electromyographic activity was recorded continuously from the lumbar paraspinal, gluteus maximus, and biceps femoris muscles during isotonic trunk extension exercise performed to muscular failure. Root mean squared electromyography was determined over the concentric portion of each repetition, and polynomial regression analysis was used to describe the association between fatigue and the recruitment patterns. Results. The lumbar paraspinals demonstrated an increase in the electromyogram signal up to 57.9% of maximal fatigue, at which point decrements in electromyography were observed (lumbar [quadratic curve] R2 = 0.0807, SEE = 0.228; &bgr;2 = −8.245−5) (P < 0.000). Associated with fatigue, the gluteus maximus demonstrated an increase in electromyography, with an exponential breakpoint occurring at 35.9% of maximal fatigue (gluteus maximus [quadratic curve]: R2 = 0.5059, SEE = 0.865; &bgr;2 = 0.00017) (P = 0.014). The biceps femoris demonstrated a linear increase in electromyography with fatigue (R2 = 0.4667, SEE = 0.284; &bgr; = 0.0091) (P < 0.000). To further investigate the derecruitment of the lumbar extensors associated with fatigue, study participants were analyzed individually with regression analyses. Results revealed that the majority of study participants (68.5%) demonstrated a significant decrease (quadratic bend) in lumbar electromyography, with decrements in muscle activity beginning at 53% of maximum. Conclusion. During fatiguing trunk extension exercise, an increase in the lumbar paraspinal electromyogram signal occurs up to approximately 55% of maximum fatigue, at which point a decrease in electromyography is observed. Associated with this derecruitment is a concomitant increase in hip extensor muscle activity, suggesting that as the lumbar musculature becomes fatigued, these muscles allow for continuation of the exercise.

Gastric gas and fluid emptying assessed by magnetic resonance imaging

Abstract Magnetic resonance imaging (MRI) was used to characterize the volumes and rates of gastric emptying of both liquid and gas following the ingestion of beverages of varying carbonation and carbohydrate levels. Eight subjects drank 800 ml each of four test beverages in a counterbalanced order: water, a non-carbonated carbohydrate-electrolyte solution (NC), a lightly carbonated carbohydrate-electrolyte solution (PC), and a carbonated cola (CC). T2-weighted, echoplanar images (25–30 contiguous slices, 1 cm thick, 256 × 128 matrix, TE = 80, 40 cm FOV) of the abdomen were collected at minutes 3,110, 20, 30, 45, and 60 following beverage ingestion. Images were analyzed for gas and liquid volumes. Water and NC emptied the most rapidly, with half times of 21(3) and 31(3) min, respectively [mean (SE)]. PC emptied significantly slower [47 (6) min] and CC slower yet [107 (8) min]. The carbonation content of the beverage accounted for 84% of the variation in emptying time, whereas carbohydrate content did not account for any significant variation. The gastric gas volume of the CC was higher at 2 min post-ingestion compared with all other drinks; however, the rate of emptying of the gas was the same among all beverages. Significantly greater total gastric volumes (gas+liquid) were associated with the ingestion of CC, and accordingly produced a greater severity of gastric distress, as evaluated with a gastric distress inventory. The high gastric gas volumes (≈600 ml) after ingestion of CC suggested a potential source of error in body composition using standard hydrostatic weighing methods. This prediction was tested in nine additional subjects. Ingestion of 800 ml of CC prior to hydrostatic weighing resulted in a 0.7% underestimate of body density and thus an 11% overestimate of percentage body fat compared to measurements made before beverage consumption.

The effect of progressive resistance training on leg strength, aerobic capacity and functional tasks of daily living in persons with Down syndrome

Purpose. The purpose of this study was to examine the effect of progressive resistance training on leg strength, aerobic capacity and physical function in persons with Down syndrome (DS). Method. Thirty persons with DS (age 28 SD 8 years) were assigned to an intervention or control group. The intervention group performed resistance training 2 days per week for 10 weeks. Participants performed tests to measure isometric and isokinetic knee extensor and flexor peak torque, peak aerobic capacity and timed performance on chair rise, walking and stair ascent and descent. Result. Persons with DS receiving the intervention significantly increased their isokinetic knee extensor and flexor peak torque [[Absolute change (post minus pre-value) was 17.0 SD 29.6 and 12.6 SD 18.9 N m, respectively]] and isometric knee extensor peak torque at angles of 45° (2.9 SD 23.2 N m), 60° (3.0 SD 22.9 N m) and 75° (14.2 SD 30.0 N m). These changes were significantly greater than in the control group. In addition, the time to ascend (−0.3 SD 0.8 s) and descend (−0.6 SD 0.9 s) stairs significantly decreased in the intervention group compared to the control group. Conclusion. These findings show that progressive resistance training is an effective intervention for persons with DS to improve leg strength and stair-climbing ability.

RELIABILITY OF KNEE AND ANKLE STRENGTH MEASURES IN AN OLDER ADULT POPULATION

Strength training for older adults is increasingly common, yet surprisingly little research has evaluated the reliability of strength testing protocols in this population. Thirty-three volunteers (17 women, 16 men; 72 ± 6 years) were tested for strength of the knee and ankle using a Biodex 3 dynamometer on 3 separate occasions. The peak torque and work for each test was analyzed for reliability over the last 2 visits using limits of agreement (LOA). The magnitude of the systematic bias was 8 Nm or less for the peak torque and 5 J or less for the work measures. The random error ranged from 9 to 20 Nm and 6 to 24 J for peak torque and work, respectively. Heteroscedasticity was present in 8 of the 20 measures. The ratio LOA ranged from 21% to 43% for these peak torque and work measures. The total error of each strength measure, which was mostly comprised of random error, can be applied to interpretation and development of training protocols for the older adult.

Increased vulnerability to eccentric exercise-induced dysfunction and muscle injury after concentric training

OBJECTIVE To test whether concentric (CON)-only resistance training increases the vulnerability to eccentric (ECC) exercise-induced dysfunction and muscle injury. DESIGN Before-after trial. SETTING General community. PATIENTS OR OTHER PARTICIPANTS Nine men (77 +/- 3 kg body weight) who were not trained in resistance exercise. INTERVENTION Nine weeks of CON-only training of the left quadriceps femoris (QF); performance of 10 sets of 10 ECC actions with each QF using a load equivalent to 85% of the posttraining CON 1-repetition maximum (1RM). MAIN OUTCOME MEASURES CON 1RM for the untrained and trained QF measured immediately after training, and again 1, 3, 8, and 10 days after the bout of ECC exercise; cross-sectional area and spin-spin relaxation time (T2) of each QF determined by magnetic resonance imaging (MRI) before and 3 days after the ECC exercise bout. RESULTS As a result of the ECC bout, the CON 1RM was reduced by approximately 30% in the trained limb and 16% in the untrained limb. Strength did not return to normal in the trained limb even after 10 days of recovery; however, in the untrained limb strength was restored by day 8. As assessed by MRI, the trained limb showed a greater area of muscle injury compared with the untrained QF. The T2 of the injured area was similar in both limbs, suggesting that the intensity of injury was similar, but more widespread in the trained limb. CONCLUSION CON-only training increases the vulnerability to ECC exercise-induced dysfunction and muscle injury, probably by increasing the CON 1RM, thus allowing the individual to be exposed to greater ECC loading potential.