What is the evidence for productivity benefits of weightlifting?

I split my findings into categories and bolded the parts of the studies I found most interesting. I really didn't take the time to be super critical on study design, etc; I was just taking their findings at face value and seeing what, if the study was true as reported, was being claimed. Enjoy!

1. Sleep

• https://www.sciencedirect.com/science/article/pii/S1087079216301526
• Claim: “Chronic resistance exercise improves all aspects of sleep, with the greatest benefit for sleep quality. These benefits of isolated resistance exercise are attenuated when resistance exercise is combined with aerobic exercise and compared to aerobic exercise alone”
• “Improvements in sleep quality were observed across all intensities, however, effect sizes for all sleep quality outcomes (significant and non-significant) tend to be larger in studies of high intensity exercise”
• The least benefit was sleep duration
• Sleep quality was ‘perceived sleep quality’ - measured by subjective ratings
• Chronic here means avg. Of 14 weeks with an average of 60 min per session
• “There is limited evidence that combined exercise is better than aerobic exercise alone, and further study is warranted. Data from this review and recent reviews of aerobic exercise [44, 57] suggest that both modalities are effective for improving sleep quality “

2. Cognitive Function

• The impact of behavioral interventions on cognitive function in healthy older adults: A systematic review
• https://www.sciencedirect.com/science/article/pii/S1568163718301831?via%3Dihub
• “Numerous experimental studies have demonstrated that exercise interventions improve cognitive abilities (Kelly et al., 2014b), but benefits have been more consistent for aerobic training, or combined cardiovascular fitness and resistance training”
• “Aerobic training (n= 13) most consistently transferred to executive function, while strength/resistance training (n = 8) most consistently transferred to cognitive inhibition and visual working memory. Similarly, aerobic/resistance combination training (n = 6) showed most consistent improvements in visual working memory”
• Acute Effects of Resistance Exercise on Cognitive Function in Healthy Adults: A Systematic Review with Multilevel Meta-Analysis.
• https://www.ncbi.nlm.nih.gov/pubmed/30838520
• “Compared to NEX, RE had a positive effect on global cognition (SMD: 0.56, 95% CI 0.22–0.90, p = 0.004), but was not superior to AE (SMD: − 0.10, 95% CI 0.01 to − 0.20, p = 0.06)”
• NEX = no exercise; AE = aerobic exercise, RE = resistance exercise
• “Regarding cognitive sub-domains, RE, compared to NEX, improved inhibitory control (SMD: 0.73, 95% CI 0.21–1.26, p = 0.01) and cognitive flexibility (SMD: 0.36, 95% CI 0.17–0.55, p = 0.004)”
• Note — the reference to cognitive inhibition was referred to by the study above as well. Kind of interesting.
• “Our review detected no difference between RE and AE in acute effects on brain function. This result is in line with the meta-analysis of Northey et al. [15], who investigated the effects of chronic exercise on cognition in adults aged 50 years and older.”
• Lifting cognition: a meta-analysis of effects of resistance exercise on cognition
• https://www.ncbi.nlm.nih.gov/pubmed/30627769
• Positive effects on composite cognitive scores, screening measures of cognitive impairments, and executive functions. no effect on measures of working memory.
• “High heterogeneity was observed in all analyses” and the authors weren’t sure why
• Long-Term Effects of Resistance Exercise Training on Cognition and Brain Volume in Older Women: Results from a Randomized Controlled Trial.
• https://www.ncbi.nlm.nih.gov/pubmed/26581787
• Aerobic exercise training has been shown to attenuate cognitive decline and reduce brain atrophy with advancing age. The extent to which resistance exercise training improves cognition and prevents brain atrophy is less known, and few studies include long-term follow-up cognitive and neuroimaging assessments. We report data from a randomized controlled trial of 155 older women, who engaged in 52 weeks of resistance training (either once- or twice-weekly) or balance-and-toning (twice-weekly). Executive functioning and memory were assessed at baseline, 1-year follow-up (i.e., immediately post-intervention), and 2-year follow-up. A subset underwent structural magnetic resonance imaging scans at those time points. At 2-year follow-up, both frequencies of resistance training promoted executive function compared to balance-and-toning (standardized difference [d]=.31-.48). Additionally, twice-weekly resistance training promoted memory (d=.45), reduced cortical white matter atrophy (d=.45), and increased peak muscle power (d=.27) at 2-year follow-up relative to balance-and-toning. These effects were independent of one another. These findings suggest resistance training may have a long-term impact on cognition and white matter volume in older women.

3. Fatigue

• Exercise to reduce work-related fatigue among employees: a randomized controlled trial
• Note: This is evidence relating to aerobic, not resistance, exercise.
• http://www.sjweh.fi/show_abstract.php?abstract_id=3634
• “Analyses of covariance (ANCOVA) revealed that, at T1, the EI group reported lower emotional exhaustion and overall fatigue than the WLC group, however, only according to PP analyses. Both according to ITT and PP analyses, EI participants showed higher sleep quality, work ability, and self-reported cognitive functioning at T1 compared to WLC participants. Intervention effects were maintained at T2 and T3.”
• “The exercise intervention consisted of 1-hour low- intensity running sessions three times a week for a period of six consecutive weeks.”
• Exercise, inflammation, and fatigue in cancer survivors
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4755327/
• Might be hard to generalize, but just thought it was interesting to point out another setting where exercise reduced fatigue
• Effects of Different Exercise Modalities on Fatigue in Prostate Cancer Patients Undergoing Androgen Deprivation Therapy: A Year-long Randomised Controlled Trial.
• https://www.ncbi.nlm.nih.gov/pubmed/28249801
• “Different exercise modes have comparable effects on reducing fatigue and enhancing vitality during ADT. Patients with the highest levels of fatigue and lowest vitality had the greatest benefits.”

4. Stuff I didn’t understand but maybe someone else does

• The effects of physical activity and exercise on brain-derived neurotrophic factor in healthy humans: A review
• https://www.ncbi.nlm.nih.gov/pubmed/23600729
• “Evidence from experimental studies suggested that peripheral BDNF concentrations were elevated by acute and chronic aerobic exercise. The majority of the studies suggested that strength training had no influence on peripheral BDNF. The results from most observational studies suggested an inverse relationship between the peripheral BDNF level and habitual physical activity or cardiorespiratory fitness. “
• I just included this because I have vague memories of BDNF being related to the psychological effect of exercise, but I'm not well informed enough on this to know the implications.

Takeaways:

• There does seem to be some effect of resistance training on cognition. These studies separated cognition into a number of subfields (executive function, visual working memory, etc).
• Every time I saw a mention of a study that did a controlled comparison of resistance training+aerobic exercise to resistance training alone, the study concluded that these were similar. It really gave me the sense that when it comes to cognitive benefits and fatigue, high intensity aerobic exercise provides the benefit, and resistance training, if it includes high intensity aerobic exercise, can capture that benefit.
• The one cognitive effect that was captured by resistance training but not aerobic exercise was cognitive inhibition, which another study also mentioned. I didn't have time to check how robust a result that was.

One final comment - while I couldn't really make a strong case for resistance training being obviously better than aerobic training with respect to productivity in any manner, I still think that 1) resistance training probably does have absolute benefits to cognition and energy levels, and 2) there are many reasons to pursue resistance training outside of productivity (for instance, things like osteoporosis risk didn't come up in a productivity-related search, but would be relevant when I design my own workout plan).

There is some indirect evidence that weightlifting improves productivity, assuming that cognition is an important determinate of productivity.

For example, a recent meta-study, Lifting cognition: a meta-analysis of effects of resistance exercise on cognition by Jon-Frederick Landrigan, Tyler Bell, Michael Crowe, Olivio J. Clay, Daniel Mirman, reports that:

Results revealed positive effects of resistance training on composite cognitive scores (SMD 0.71, 95% CI 0.30-1.12), screening measures of cognitive impairment (SMD 1.28, 95% CI 0.39-2.18), and executive functions (SMD 0.39, 95% CI 0.04-0.74), but no effect on measures of working memory (SMD 0.151, 95% CI - 0.21 to 0.51).

List of papers

Some incremental progress, just taking the obvious first action of "search google scholar for 'benefits of exercise on productivity'", followed by a search for "benefits of strength training on productivity" after remembering that the first one wasn't quite right (but maybe still useful enough to include)

Including random quotes that seemed most relevant (did not search anything very hard)

Does strength training programme improve work task performance in young adults with Down Syndrome?

https://bmcpediatr.biomedcentral.com/articles/10.1186/1471-2431-10-17

The effect of the PRT programme on work task performance will be assessed using two tests (a) repetitive weighted box stacking and (b) weight carry test (pail carry). The repetitive weighted box stacking test requires the participants to repetitively lift 10 kg boxes, from the floor to a table 75 cm off the ground. The number of boxes stacked in one minute is measured. The weighted pail carry requires participants to carry two 20 litre buckets each weighing 10 kg around an oblong 10 m course marked with cones. The total distance covered in 30 seconds is measured in metres. Running is not permitted for safety reasons. These measures are recommended by the American College of Sports Medicine [33] and have demonstrated changes in people with intellectual disability [34, 35].

The impact of a self-paced exercise program on productivity and health outcomes of 32 adult workers in a large federal office complex was investigated during 3 months.

https://journals.sagepub.com/doi/pdf/10.1177/216507990705500302

Walking was the sole form of exercise. The first month, during which no walking occurred, was the control period. The second and third months were the experimental period. Participants were divided into three levels based on initial weight and self-determined walking distance goals. Productivity (using the Endicott Work Productivity Scale), walking distance (using a pedometer), and health outcomes (blood pressure, weight, pulse rate, and body fat percentage) were measured weekly. Results from this study, based on a paired t test analysis, suggest that although the self-paced exercise program had no impact on productivity, it lowered blood pressure and promoted weight loss. Further study using a larger sample and a controlled experimental design is recommended to provide conclusive evidence.

Exercise is more than medicine: The working age population's well-being and productivity

https://www.sciencedirect.com/science/article/pii/S2095254616300096

In Denmark 15 randomized controlled trials have been conducted, introducing exercise at the workplace enrolling >3500 workers. The interventions lasted from 10 to 52 weeks and offered ~1 h weekly supervised exercise during working hoursaccording to the concept of intelligent physical exercise training (IPET) that is based on evidenced sports sciences training principles and tailored to work exposure, employee health status, and physical capacity. Questionnaire surveys and health checks including blood and muscle sampling were performed at baseline and follow-up. The job groups included: office and computer workers, dentists, industrial technicians, cleaning personnel, health care workers, construction workers, and fighter/helicopter pilots.

[...]

Poor health among employees implies substantial costs for the companies. The costs relate to increased sickness presenteeism (decreased on-the-job-performance while being at the workplace) as well as absenteeism (habitual absence from work) leading to loss of work productivity.37 Sickness presenteeism was assessed as self-reported on-the-job-performance, using questions in regard to productivity, work ability, and quantity and quality of work.

Importantly, in spite of spending 1 h a week performing physical exercise training during work time, in none of our studies we found a decrease in the variables underlying on-the-job-performance.

However, we did, in an intention-to-treat analysis, find a significant 8% increase in productivity of the intervention among health care workers after 3 months but not after 1 year of intervention.38 Likewise among dentists we found improved self-reported quality of work.18

Interestingly, some exploratory analysis of our RCTs actually revealed some relevant findings: productivity increased with decreased neck/shoulder pain, and with improved muscle strength—in particular trunkflexion and extension—as well as decreased BMI among health care workers.37Further, workers with sedentary monotonous tasks (office/computer) —who were physically active at leisure compared with those being inactive—perceived less stress and more energy. These perceived differences were underlined by corresponding differences in physiological measures of the stress-hormonecortisol.39 Regarding sickness absenteeism analysis on our RCTs so far has not identified significant changes with the interventions.

The Benefits of Exercise for the Clinically Depressed

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC474733/

While most studies have employed walking or jogging programs of varying lengths, the efficacy of nonaerobic exercise has also been assessed. For example, in comparison with a control condition, resistance-training programs reduced symptoms of depression (resistance training vs. control resulted in BDI reduction of 11.5 vs. 4.6, respectively, p < .01, and HAM-D reduction of 7.0 vs. 2.5, respectively, p < .01).21

Aerobic and nonaerobic modes of exercise have also been compared to determine if certain types of activities are more effective than others. Doyne and colleagues22 compared the efficacy of running with that of weight lifting. Forty depressed women served as participants and were randomly assigned to running, weight lifting, or a wait-list control group. Participants were asked to complete 4 training sessions each week for the 8 weeks of the program. Depression was assessed at mid- and post-treatment and at 1, 7, and 12 months follow-up. Results indicated that the 2 activities were not significantly different, and that both types of exercise were sufficient to reduce symptoms of depression (running vs. weights vs. control resulted in BDI reduction of 11.1 vs. 13.6 vs. 0.8, respectively, p < .01, and HAM-D reduction of 6.7 vs. 8.7 vs. a 1.0 increase, respectively, p < .01).

Further, there were no differences between the 2 treatment groups during follow-up with respect to the percentage of participants who remained nondepressed. Similarly, a study by Martinsen et al.23 assessed 90 depressed in-patients who were randomly assigned to aerobic or non-aerobic exercise. Aerobic exercise consisted of jogging or brisk walking, and nonaerobic exercise included strength training, relaxation, coordination, and flexibility training. The program was 8 weeks in length, and participants exercised for 60 minutes, 3 times per week. Those in the aerobic group exhibited an increase in PWC compared with those in the nonaerobic group. However, both groups experienced a significant reduction in depression score (p < .001), but there were no significant differences between the groups with respect to the magnitude of change in depression score (p > .10).

Extremely strong.

... I'll see myself out.

My personal experience: exercising makes me feel better. One can't do much when he feels bad, right? Hence I believe that exercising makes one more productive. It helps me to cope with depression, too. I might feel very terrible sometimes, and in such moments exercising is what helps me to get back on track. Without exercising one will rot, I think. Exercising is good, in moderate measures.