95% Reduced CK (Marker of Muscle Damage) + Pain After Eccentric Curls W/ Ischemic Pre-Conditioning (3x5min BFR)

In the study at hand, the cuffs were applied before, not during the exercise.

This is not the first and it's certainly not going to be the last SuppVersity article about blood flow restriction (BFR). In contrast to previous articles, today's blog post does yet not focus on the effects of acute blood flow restriction on performance or gains. Rather than that, it discusses a recent study from the University Hospital of Düsseldorf (Germany), the Göthe University in Frankfurt, and the German Sport University in Cologne which investigated the effects of so-called "ischemic preconditioning" (which could be described as pre-workout BFR) on muscle damage and pain in response to eccentric biceps curls.
As Franz, et al., the authors of the study that is about to be published in "Medicine & Science in Sports & Exercise", ischemic preconditioning (IPC) is known to reduce muscle damage induced by ischemia and reperfusion-injury (I/R-Injury) during surgery - in that case, however, we are talking about damage to organs like the heart (Walsh 2008; Takagi 2008; D'ascenzo 2012). The German scientists did yet simply assume that ...

[d]ue to similarities between the pathophysiological formation of I/R-injury and eccentric exercise-induced muscle damage (EIMD), as characterized by an intracellular accumulation of Ca2+, an increased production of reactive oxygen species and increased pro-inflammatory signaling, [...] IPC performed prior to eccentric exercise may also protect against EIMD [exercise induced muscle damage]" (Franz 2017).

To confirm or falsify this assumption Fritz et al. recruited nineteen untrained healthy men and had them perform a standardized exercise protocol consisting of bilateral biceps curls (3x10 repetitions at 80% of the concentric 1RM), during which the subjects were assisted on the concentric part of the exercise until they reached an elbow flexion of ~50°.  To accommodate for the previously discussed high inter-personal variability in subjects' creatine kinase [~muscle damage] response to exercise, the authors matched their subjects to the preconditioning (IPC+ECC) and control (ECC) group based on their CK response to an identical 1-RM test all participants had to do before the actual experiment.
The ischemic preconditioning (IPC) was applied bilaterally at the upper arms by a tourniquet (200 mmHg) immediately prior to the exercise (3x5 minutes of occlusion, separated by 5 minutes of reperfusion). Creatine Kinase (CK), arm circumference, subjective pain (VAS score) and radial displacement (Tensiomyography, Dm) were assessed before IPC, pre-exercise, post-exercise, 20 minutes-, 2 hours-, 24 hours-, 48 hours- and 72 hours post-exercise.

Figure 1: Graphical overview o the study design.

In addition, the development of reversible muscle swelling was monitored by assessing the circumference of the dominant arm at the mid-portion of the upper arm, defined as 50% of the length between the acromion process and the lateral epicondyle of the humerus. Subjective pain intensity was recorded on a 100-mm visual analog score (VAS).

Figure 2: Creatine kinase (U/L) and arm circumference (cm) in the hours/days after the eccentric workout (Fritz 2017).

As it was to be expected base on what you've learned about CK at the SuppVersity, it took some time for the changes in CK to become significant. More specifically, ...

• CK differed from baseline only in ECC at 48h (p<0.001) and 72h (p<0.001) post-exercise, 
• after 24h, 48h and 72h, CK was increased in ECC compared to IPC+ECC (between groups: 24h: p=0.004, 48h: p<0.001, 72h: p<0.001). 

The post-exercise pain intensity VAS was likewise attenuated by IPC with significantly lower values for IPC+ECC 24-72 h post-exercise (between groups: all p<0.001).

The swelling of the arm(s), on the other hand, did not differ significantly. Since the same goes the muscle contractility that was measured by tensiomyography it is, in the absence of data on the short-term effects on muscle recovery and potential long-term effects on gains, difficult to tell how much of an advantage the impressive reduction in markers of muscle damage actually is.
References:

• D'ascenzo, Fabrizio, et al. "Remote ischaemic preconditioning in coronary artery bypass surgery: a meta-analysis." Heart 98.17 (2012): 1267-1271.
• Hong, Yang, et al. "Cell membrane integrity and revascularization: The possible functional mechanism of ischemic preconditioning for skeletal muscle protection against ischemic-reperfusion injury." Acta Histochemica 119.3 (2017): 309-314.
• Walsh, Stewart R., et al. "Ischaemic preconditioning during cardiac surgery: systematic review and meta-analysis of perioperative outcomes in randomised clinical trials." European Journal of Cardio-Thoracic Surgery 34.5 (2008): 985-994.
• Takagi, Hisato, et al. "Review and meta-analysis of randomized controlled clinical trials of remote ischemic preconditioning in cardiovascular surgery." The American journal of cardiology 102.11 (2008): 1487-1488.