The impact of inertial exercises performed in the workplace on shoulder muscles' strength and muscles' fatigue resistance in women with disabilities

BACKGROUND

Workers who do monotonous and repetitive work in a static position often complain about fatigue and decreased work efficiency. Some studies indicate that to improve muscle fatigue, resistance strength training can be used.

MATERIAL AND METHODS

To investigate the effect of 4-week inertial training on shoulder muscles' strength and muscles' fatigue resistance 44 female workers with disabilities were examined. The participants were randomized into the training group (T) (N = 32) and the control group (C) (N = 12). Before the training and after that shoulder muscles' strength were tested at the start and at the end of the workday (Monday and Friday). The participants were asked to complete questionnaire concerning their fatigue at work (T and C), inertial training and work efficiency (T).

RESULTS

The work performed during the last day of the workweek, i.e., Friday (before training) resulted in a significant decrease in shoulder muscles' strength in T and C. Muscle strength achieved at the end of the workweek (Friday afternoon) was significantly lower than achieved at the start of the workweek (Monday morning) in both tested groups (before training). Moreover, inertial training resulted in a significant increase in shoulder muscles' strength in T; 34-74% for different muscles. No changes in muscles' strength were noted in C. Increased muscle strength in T following inertial training effectively prevented muscle fatigue. After training the differences in shoulder muscles' strength noted in T during different times of the workday and workweek were insignificant. Moreover, 4-week inertial training increased significantly the work efficiency of women from T by 4%; no changes were noted in C. Inertial training was well tolerated by the participants.

CONCLUSIONS

We recommend using inertial training in women with disabilities to prevent shoulder muscles' fatigue during the workday and workweek. Med Pr Work Health Saf. 2024;75(2).

Effects of 8-Week Exhausting Deep Knee Flexion Flywheel Training on Persistent Quadriceps Weakness in Well-Trained Athletes Following Anterior Cruciate Ligament Reconstruction

Persistent quadriceps weakness after anterior cruciate ligament (ACL) reconstruction is a common hurdle to efficient rehabilitation. Therefore, we evaluated a new treatment strategy for athletes with ACL reconstruction. Eleven athletes with unilateral ACL reconstruction performed one set of flywheel Bulgarian split squats to exhaustion with a maximum knee extension of 60°, over 16 sessions, on their reconstructed limb. Quadriceps rate of force development (RFD) 0-50 ms (RFD_{0-50 ms}), and 0-150 ms (RFD_{0-150 ms}), maximum voluntary isometric contraction (MVIC), and central activation ratio (CAR) were measured bilaterally on the week before and after the intervention. In the reconstructed limb, the RFD_{0-50 ms} (p = 0.04; Cohen's d = 0.8) and RFD_{0-150 ms} (p = 0.03; d = 0.9) increased after training. Before-after changes in MVIC and CAR were not significant (p > 0.05), but the lower the baseline MVIC, the greater the gain in MVIC (r = -0.71, p = 0.02). The between-leg difference in MVIC changed from large before (p = 0.01; d = 0.8) to small after training (p = 0.04; d = 0.4). One set of deep knee flexion flywheel Bulgarian split squats to exhaustion improved quadriceps deficits in well-trained athletes with ACL-reconstruction, particularly those with relatively low quadriceps force production.

Impact of Inertial Training on Muscle Strength and Quality of Life in Breast Cancer Survivors

The aim of the study was to evaluate the impact of inertial training on the muscle strength, on breast-cancer-related lymphedema, and on quality of life in breast cancer survivors. After a mastectomy, 24 women (age, 66.2 ± 10.6 years) were randomized to a training (n = 12) or control group (n = 12). The training group performed inertial training twice per week for 6 weeks with a training load of about 70% of the maximal force. Before and after training, we tested the maximum force of shoulder flexors, extensors, abductors, and adductors; body composition; breast-cancer-related lymphedema; and disabilities of the arm, shoulder, and hand. Inertial training significantly improved the strength in all tested muscles (from 32 to 68%; effect size (ES) from 0.89 to 1.85 in the impaired limb and from 31 to 64%; ES from 0.86 to 1.57 in the unimpaired limb). However, changes in the control group were not significant. Quality of life improved following treatment; the disabilities of the arm, shoulder, and hand score decreased significantly by 24.5% (ES from—0.29 to 1.38), p ≤ 0.05 in the training group and by 3.99% (ES from −0.49 to 1.14) in the control group p > 0.05. Breast-cancer-related lymphedema and body composition did not change significantly after the intervention in either group. We recommend inertial training for increasing muscle strength and improving quality of life in breast cancer survivors.

Influence of Strength Level on the Acute Post-Activation Performance Enhancement Following Flywheel and Free Weight Resistance Training

This study aimed to compare the post-activation potentiation performance enhancement (PAPE) response to the acute inertial flywheel (FW) and free weight resistance training (TRA) on subsequent countermovement jump (CMJ) and sprint performance (10 m sprint). This study used a randomized crossover design including twenty-eight healthy males that were divided into strong (relative one-repetition maximum (1RM) back squat > 2.0 × body mass) and weak (relative 1RM back squat < 2.0 × body mass) groups. All participants performed the following: (a) three reps at 90% of their 1RM back squat (TRA) and (b) three reps on an inertial FW (plus one repetition to initiate flywheel movement) with an intensity that generated a mean propulsive velocity equal to that achieved with 90% of the 1RM back squat. Before and after the conditioning activity, participants performed two CMJs and two 10 m sprints. Within-group analyses showed significantly greater CMJ (d > 0.9, p < 0.001) and sprint performance (d > 0.5, p < 0.05) in the FW and the TRA group. Between-group analysis showed that sprint changes were significantly greater in the FW-strong group when compared with the TRA (F_1,18 = 5.11, p = 0.036, η²_p = 0.221-large) group. These results suggest that using a squat activation protocol on a FW may lead to an acute positive effect on jump and sprint performance, especially in stronger individuals.