Dain P. LaRoche

Strength asymmetry increases gait asymmetry and variability in older women.

PURPOSE The aim of the research was to determine how knee extensor strength asymmetry influences gait asymmetry and variability because these gait parameters have been related to mobility and falls in older adults. METHODS Strength of the knee extensors was measured in 24 older women (65-80 yr). Subjects were separated into symmetrical strength (SS, n = 13) and asymmetrical strength (SA, n = 11) groups using an asymmetry cutoff of 20%. Subjects walked at a standard speed of 0.8 m·s and at maximal speed on an instrumented treadmill while kinetic and spatiotemporal gait variables were measured. Gait and strength asymmetry were calculated as the percentage difference between legs and gait variability as the coefficient of variation over 20 sequential steps. RESULTS SA had greater strength asymmetry (27.4% ± 5.5%) than SS (11.7% ± 5.4%, P < 0.001). Averaged across speeds, SA had greater single- (7.1% vs. 2.5%) and double-limb support time asymmetry (7.0% vs. 4.3%) than SS and greater single-limb support time variability (9.7% vs. 6.6%, all P < 0.05). Group × speed interactions occurred for weight acceptance force variability (P = 0.02) and weight acceptance force asymmetry (P = 0.017) with greater variability at the maximal speed in SA (5.0% ± 2.4% vs. 3.7% ± 1.2%) and greater asymmetry at the maximal speed in SA (6.4% ± 5.3% vs. 2.5% ± 2.3%). CONCLUSION Gait variability and asymmetry are greater in older women with strength asymmetry and increase when they walk near their maximal capacities. The maintenance of strength symmetry, or development of symmetry through unilateral exercise, may be beneficial in reducing gait asymmetry, gait variability, and fall risk in older adults.

Chronic stretching and voluntary muscle force.

The purpose of the study was to determine whether muscle force, power, and optimal length were affected by 4 weeks of static or ballistic stretching. Twenty-nine males (age, 18-60 years) performed 4 maximal hip extensions to measure peak torque (PT), rate of torque development (RTD), work (W), and PT angle (PTA). Then, participants completed 4 weeks of static or ballistic flexibility training of the hip extensors followed by repetition of the testing protocol. After training, PT increased 5.3 ± 19.0% in the static group (SG), 7.8 ± 12.7% in the ballistic group (BG), and 6.1 ± 17.9% in the control group (CG). RTD increased 4.8 ± 22.7% in the SG, 3.6 ± 28.0% in the BG and 9.7 ± 24.0% in the CG. W increased 3.9 ± 7.0% in the SG, 14.7 ± 27.4% in the BG, and 5.5 ± 9.5% in the CG. PTA changed little with a −1.6 ± 6.6% decrease in the SG and increases of 0.86 ± 4.1% in the BG and 0.18 ± 8.7% in the CG. None of the results were statistically different between stretching group and CG (α = 0.05). These data suggest that 4 weeks of stretching have little effect on muscle strength, power, W, or length-tension relationship. PTA changed little, suggesting that a lengthening of the muscle with stretching did not occur. It is suggested that individuals can routinely stretch following exercise to maintain flexibility but should avoid stretching prior to exercise requiring high levels of muscle force. Before exercise that requires high muscular forces, individuals may perform dynamic, sport-specific exercises to increase blood flow, metabolic activity, temperature, and compliance of the muscle.

3 Different Types of Strength Training in Older Women

The objective of the present study was to evaluate and compare the neuromuscular, morphological and functional adaptations of older women subjected to 3 different types of strength training. 58, healthy women (67 ± 5 year) were randomized to experimental (EG, n=41) and control groups (CG, n=17) during the first 6 weeks when the EG group performed traditional resistance exercise for the lower extremity. Afterwards, EG was divided into three specific strength training groups; a traditional group (TG, n=14), a power group (PG, n=13) that performed the concentric phase of contraction at high speed and a rapid strength group (RG, n=14) that performed a lateral box jump exercise emphasizing the stretch-shortening-cycle (SSC). Subjects trained 2 days per week through the entire 12 weeks. Following 6 weeks of generalized strength training, significant improvements occurred in EG for knee extension one-repetition (1RM) maximum strength (+19%), knee extensor muscle thickness (MT, +15%), maximal muscle activation (+44% average) and onset latency ( -31% average) for vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) compared to CG (p<0.05). Following 6 more weeks of specific strength training, the 1RM increased significantly and similarly between groups (average of +21%), as did muscle thickness of the VL (+25%), and activation of VL (+44%) and VM (+26%). The onset latency of RF (TG=285 ± 109 ms, PG=252 ± 76 ms, RG=203 ± 43 ms), reaction time (TG=366 ± 99 ms, PG=274 ± 76 ms, RG=201 ± 41 ms), 30-s chair stand (TG=18 ± 3, PG=18 ± 1, RG=21 ± 2) and counter movement jump (TG=8 ± 2 cm, PG=10 ± 3 cm, RG=13 ± 2 cm) was significantly improved only in RG (p<0.05). At the end of training, the rate of force development (RFD) over 150 ms (TG=2.3 ± 9.8 N·s(-1), PG=3.3 ± 3.2 N·s(-1), RG=3.8 ± 6.8 N·s(-1), CG=2.3 ± 7.0 N·s(-1)) was significantly greater in RG and PG than in TG and CG (p<0.05). In conclusion, rapid strength training is more effective for the development of rapid force production of muscle than other specific types of strength training and by consequence, better develops the functional capabilities of older women.

Low strength is related to diminished ground reaction forces and walking performance in older women

The purpose of this study was to determine how lower-limb strength in older women affected gait speed, supportive forces, spatial, and temporal aspects of walking gait. Twenty-four women between 65 and 80 yr performed maximal voluntary isometric contractions for the knee extensors (KE), knee flexors (KF), ankle plantarflexors (PF) and ankle dorsiflexors (DF) and were separated into low strength and normal strength groups using a KE torque threshold of 1.5 Nm kg(-1). They walked at both a standard speed of 0.8 m s(-1) and at a self-selected maximal speed on an instrumented treadmill that recorded vertical ground reaction forces (vGRF) and spatiotemporal gait measures. Older women with low strength had 30% lower KE maximal torque, 36% lower PF maximal torque, 34% lower KE rate of torque development (RTD) and 30% lower KF RTD. Low strength women demonstrated slower maximal walking speeds (1.26±0.20 m s(-1) vs. 1.56±0.20 m s(-1)), lower vGRF during weight acceptance (1.15±0.10 BW vs. 1.27±0.13 BW), lower weight acceptance rates (11.3±0.5 BW s(-1) vs. 17.0±5.5 BW s(-1)), slower stride rates, shorter stride lengths, and longer foot-ground and double-limb support times (all P<0.05). Maximal gait speed was strongly correlated to peak vGRF and rate (r=0.60-0.85, P<0.01) and moderately related to lower-limb strength (r=0.42-0.60, P<0.05). In older women with low strength, diminished peak vGRFs were associated with slower walking speeds putting them at risk for mobility limitation, disability, poor health, and loss of independence.

Association between energy cost of walking, muscle activation, and biomechanical parameters in older female fallers and non-fallers

OBJECTIVE To determine the nervous activation, muscle strength, and biomechanical parameters that influence the cost of walking in older fallers and non-fallers. METHODS Maximal voluntary isokinetic torque was measured for the hip, knee and ankle of older women. Oxygen consumption was measured at rest and during 8min of walking at self-selected speed. An additional minute of walking was performed to collect kinematic variables and the electromyographic signal of trunk, hip, knee, and ankle muscles, which was analyzed by the linear envelope. Cost of walking was calculated by subtracting resting body mass-normalized oxygen consumption from walking body mass-normalized oxygen consumption. Stride time and length, and ankle and hip range of motion were calculated from kinematic data. FINDINGS Older adult fallers had 28% lower knee extensor strength (p=0.02), 47% lower internal oblique activation at heel contact (p=0.03), and higher coactivation between tibialis anterior and gastrocnemius lateralis in each of the gait phases (p<0.05). For fallers, a higher activation of gluteus maximus was associated with a higher cost of walking (r=0.55, p<0.05 and r=0.71, p<0.01, before and after heel contact, respectively). For non-fallers, an association between cost of walking and age (r=0.60, p=0.01) and cost of walking and thigh muscle coactivation (r=0.53, p=0.01) existed. INTERPRETATION This study demonstrated that there may be links between lower-extremity muscle weakness, muscle activation patterns, altered gait, and increased cost of walking in older fallers.

Defining Intensity Domains from the End Power of a 3-min All-out Cycling Test

PURPOSE The purpose of this study was to develop a modified version of a 3-min all-out cycling test (3MT) using equipment readily available to cyclists and to identify exercise intensity domains using the average power output over the last 30 s of the 3MT (end-test power (EP)). METHODS Sixteen competitive cyclists (V(O2peak) = 60.3 +/- 8.3 mL.kg.min) completed three laboratory visits using their own bicycles and a power-measuring rear wheel. In visit 1, subjects performed an incremental load test to volitional termination on an electronically braked trainer (100 + 25 W every 4 min). Power output at lactate threshold was determined by absolute 4 mmol.L (OBLA-PO) and 1 mmol.L over exercise baseline (LT-PO). Power output at ventilatory threshold (VT-PO) was computed on the basis of the V-slope method. Power output at V(O2peak) (V(O2peak)-PO) was the mean power observed during the stage at which peak O2 consumption was recorded. In visits 2 and 3, subjects performed the 3MT using a progressive resistance trainer with Visit 2 as a familiarization trial. During Visit 3, EP was recorded. RESULTS EP (273 +/- 52 W) was significantly greater than VT-PO, OBLA-PO, and LT-PO (232 +/- 64, 235 +/- 54, and 208 +/- 45 W, respectively) but significantly less than V(O2peak)-PO (288 +/- 56 W). EP was correlated with V(O2peak)-PO (r = 0.97), VT-PO (r = 0.87), OBLA-PO (r = 0.85), and LT-PO (r = 0.79) with regression estimates through the origin made using 105%, 86%, 86%, and 76% of EP, respectively. Demarcations for moderate- to heavy-intensity (LT-PO at 76% EP) and heavy- to severe-intensity (100% EP) domains may be estimated. CONCLUSION The 3MT can be used to define exercise intensity in competitive cyclists using readily available equipment.

Fat mass limits lower-extremity relative strength and maximal walking performance in older women

The purpose of this study was to determine if excess fat negatively affects relative strength and walking gait performance in overweight, older women. Twenty-five older women (65-80 yr) were separated into normal weight (BMI<25 kg m(-2), n=11) and overweight groups (BMI 25 ≥ kg m(-2), n=14). Strength and rate of torque development (RTD) of the knee extensors and flexors, ankle plantarflexors and dorsiflexors were measured. Participants walked at standard and maximal speeds during which muscle activation, spatiotemporal and kinetic gait variables were measured. Relative to mass, overweight older women had 24% lower maximal torque and 38% lower RTD than normal weight women. Maximal walking speed was slower in overweight (1.25±0.22 vs. 1.54±0.25 m s(-1), P=0.004) and was correlated to strength (r=0.53, P<0.01) and fat mass (r=-0.65, P=0.001). At maximal speed, overweight had 11% lower vertical ground reaction force relative to mass, 8% slower stride rate, 12% shorter strides, 13% longer foot-ground contact times, 21% longer double-limb support times, 65% greater knee extensor and 78% greater plantarflexor activation (P<0.05). Overweight, older women demonstrated altered gait and reduced walking performance related to poor relative strength and rate of torque development of lower-extremity muscles.

Antagonist coactivation of trunk stabilizer muscles during Pilates exercises

The purpose of this study was to compare the antagonist coactivation of the local and global trunk muscles during mat-based exercises of Skilled Modern Pilates. Twelve women performed five exercises and concurrently, surface EMG from internal oblique (OI), multifidus (MU), rectus abdominis (RA) and iliocostalis lumborum (IL) muscles was recorded bilaterally. The percentage of antagonist coactivation between local (OI/MU) and global muscles (RA/IL) was calculated. Individuals new to the practice of these exercises showed differences in coactivation of the trunk muscles between the exercises and these results were not similar bilaterally. Thus, in clinical practice, the therapist should be aware of factors such as compensation and undesirable rotation movements of the trunk. Moreover, the coactivation of global muscles was higher bilaterally in all exercises analyzed. This suggests that the exercises of Skilled Modern Pilates only should be performed after appropriate learning and correct execution of all principles, mainly the Centering Principle.

Excess body weight and gait influence energy cost of walking in older adults

PURPOSE The objective of this investigation is to study how excess body weight influences the energy cost of walking (Cw) and determine whether overweight and obese older adults self-select stride frequency to minimize Cw. METHODS Using body mass index (BMI), men and women between the ages of 65 and 80 yr were separated into normal weight (NW, BMI ≤24.9 kg·m(-2), n = 13) and overweight-obese groups (OWOB, BMI ≥25.0 kg·m(-2), n = 13). Subjects walked at 0.83 m·s on an instrumented treadmill that recorded gait parameters and completed three 6-min walking trials; at a preferred stride frequency (PSF), at +10% PSF, and at -10% PSF. Cw was determined by indirect calorimetry. Repeated-measures ANOVA was used to compare groups, and associations were tested with Pearson correlations, α = 0.05. RESULTS OWOB had 62% greater absolute Cw (301 ± 108 vs 186 ± 104 J·m, P < 0.001) and 20% greater relative Cw(kg) (3.48 ± 0.95 vs 2.91 ± 0.94 J·kg(-1)·m(-1), P = 0.046) than NW. Although PSF was not different between OWOB and NW (P = 0.626), Cw was 8% greater in OWOB at +10% PSF (P < 0.001). At PSF, OWOB spent less time in single-limb support (33.1% ± 1.5% vs. 34.9% ± 1.6 % gait cycle, P = 0.021) and more time in double-limb support (17.5% ± 1.6% vs 15.4% ± 1.4% gait cycle, P = 0.026) than NW. In OWOB, at PSF, Cw was correlated to impulse (r = -0.57, P = 0.027) and stride frequency (r = 0.51, P = 0.046). CONCLUSIONS Excess body weight is associated with greater Cw in older adults, possibly contributing to reduced mobility in overweight and obese older persons.

Asymmetry of lower-extremity force and muscle activation during knee extension and functional tasks

Strength and power asymmetries of >10% may negatively impact physical function.